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STATUS REPORTS 

ON TWELVE RAPTORS 




8 



UNITED STATES DEPARTMENT OF THE INTERIOR 

FISH AND WILDLIFE SERVICE 

Special Scientific Report - Wildlife No. 238 



Library of Congress Cataloging in Publication Data 

Evans, David L. (David Lawrence), 1949- 
Status reports on twelve raptors. 

(Special scientific report — wildlife ; no. 238) 
Bibliography: p. 

1. Birds of prey. I. Tide. II. Series. 
QL696.F3E87 333.95'8 81-17338 

AACR2 



NOTE: Use of trade names does not imply U.S. Government endorsement of commercial products. 



STATUS REPORTS ON TWELVE RAPTORS 



By David L. Evans 



r.s. 
ush* wii.nnn- 

SERVK'K 




UNITED STATES DEPARTMENT OF THE INTERIOR 

FISH AND WILDLIFE SERVICE 

Special Scientific Report- Wildlife No. 238 
Washington, D.C. • 1982 



Contents 

Page 

Abstract 1 

Introduction 1 

Acknowledgments 2 

Raptors 2 

Bald Eagle 2 

Burrowing Owl 13 

Caracara 17 

Cooper's Hawk 20 

Ferruginous Hawk 24 

Marsh Hawk 28 

Merlin 32 

Northern Aplomado Falcon 37 

Osprey 39 

Peregrine Falcon 47 

Prairie Falcon 57 

Sharp-shinned Hawk 64 

Appendix. Emergency Care for 111 and Injured Raptors 68 



Status Reports on Twelve Raptors 

by 

David L. Evans 1 

Department of Zoology 

North Dakota State University 

Fargo, North Dakota 58102 



Abstract 

This report presents the distribution, ecology, management, and status of 12 species of raptors, com- 
piled largely from the literature, and an extensive bibliography on each species. Earlier declines in the 
bald eagle (Haliaeetus leucocephalis) , Cooper's hawk (Accipiter cooperi), merlin (Falco columbarius) , 
osprev (Pandion haliaetus carolinensis) , peregrine falcon (Falco peregrinus), and the sharp-shinned 
hawk (Accipiter striatiis velox) appear to have ended with restrictions on organochlorine biocide use, 
and most populations appear to be recovering. However, continued use of organochlorine biocides in 
South and Central America has the potential of negating this positive trend. 

Depletion of fisheries due to acid rain may pose a future threat to bald eagle and osprey populations 
in some regions. Loss of essential habitat has affected declines in the caracara (Caracara cheriway) and 
western burrowing owl (Athene cunicularia hypugaea) and the disappearance of the northern 
aplomado falcon (Falco femoralis septentrionalis) from the southern United States. Most populations of 
the ferruginous hawk (Buteo regalis), marsh hawk (Circus cyaneus hudsonius), and prairie falcon 
(Falco mexicanus) appear stable; habitat loss is the most critical factor in population changes. 



Introduction 

This report presents a general overview of status, 
distribution, ecology, and management of 12 species of 
raptors suffering population declines or with inconclusive 
evidence concerning population changes. Establishing 
population estimates for raptors is difficult; logistical 
problems usually preclude efforts to assess reproduction 
and recruitment on a wide scale and the solitary nature of 
most raptor species defies adequate assessment of mor- 
tality rates. The bulk of present-day knowledge concern- 
ing population variables has come from intensive nesting 
studies on relatively small, often widely separated, areas. 
In a few species, concentrations of wintering birds offer 
additional insights into factors affecting population 
stability. For many species, migration counts at various 
migration concentration points provide the only economi- 
cally feasible information available on population trends. 
Unfortunately, variation in weather patterns contributes 
to wide fluctuations in yearly counts and only long-term 
analyses may discern meaningful trends. 



The following compilation, including selected 
references, is intended as a beginning reference point for 
those interested in raptor biology and may be of use to a 
diverse assortment of agencies in formulating policy deci- 
sions which may affect various facets of raptor ecology. 
The reports were compiled largely from the literature 
through mid-1977. Additional references were added, as 
available, through 1979. Emphasis was placed on North 
American studies; foreign references were included when 
pertinent. For purposes of brevity and conciseness, phrases 
or sentences with implied subjects rather than complete 
sentences are used in many of the descriptions. Scientific 
names for species are given on the following list. See Ap- 
pendix for captive diet and development. 



Common Name 



Scientific Name 



1 Present 
55812. 



address: 2928 Crevsolon Road, Duluth, Minnesota 



American kestrel 

Arctic ground squirrel 

Badger 

Barn owl 

Black-tailed jackrabbit 

Bobcat 

Brown jay 

Coyote 



Falco sparverius 
Spermophilus parryii 
Taxidea taxus 
Tyto alba 
Lepiis californicus 
Felis rufus 
Psilorhinus mono 
Canis latrans 



Golden eagle 

Gopher turtle 

Great horned owl 

Horned lark 

Kangaroo rat 

Northern pocket gopher 

Opossum 

Prairie chicken 

Prairie dog 

Raccoon 

Red fox 

Red-tailed hawk 

Richardson's ground squirrel 

Ringtail 

Robin 

Rock dove 

Rough-legged hawk 

Short-eared owl 

Spruce budworm 

Striped skunk 

Swainson's hawk 

Swift fox 

Thirteen-lined ground 

squirrel 
Timber wolf 

Townsend's ground squirrel 
White-necked raven 
White-tailed jackrabbit 



Aquila chrysaetos 
Gopherus polyphemus 
Bubo virginianus 
Eremophila alpestris 
Dipodomys 
Thomomys talpoides 
Didelphis marsupialis 
Tympanuchus spp. 
Cynomys spp. 
Procyon lotor 
Vtdpes vidpes 
Buteo jamaicensis 
Spermophdus richardsonii 
Bassariscus astutus 
Tardus migratorius 
Columba livia 
Buteo lagopus 
Asio flammeus 
Choristoneura fumiferana 
Mephitis mephitis 
Buteo swainsoni 
Vtdpes velox 
Spermophilus 

tridccemlineatus 
Canis lupus lycaon 
Spermophdus townsendii 
Corvus cryptoleucus 
Lepus townsendii 



Acknowledgments 

The following people added many helpful comments to 
the various reports: J. N. Layne (caracara), S. Postupal- 
sky (osprey), J. W. Grier, C. R. Sindelar, Jr., and S. 
Postupalsky (bald eagle), F. Hamerstrom (marsh hawk), 
R. T. Reynolds, C. J. Henny, and J. L. Ruos (sharp- 
shinned hawk and Cooper's hawk), L. Powers and D. S. 
Gilmer (ferruginous hawk), D. P. Hector and G. Hunt 
(aplomado falcon), S. A. Temple and B. Anderson 
(merlin), J. H. Enderson and D. D. Berger (peregrine and 
prairie falcon), and K. O. Butts and W. D. Courser (bur- 
rowing owl). J. W. Grier and S. Postupalsky also made 
many helpful suggestions on the final draft. P. T. Redig 
offered many helpful suggestions regarding rehabilita- 
tion. Eileen Bartels, Science Reference Librarian, Region 
III, U.S. Fish and Wildlife Service, was especially helpful 
in providing reference materials. Lynda Garrett, Li- 
brarian, Patuxent Wildlife Research Center, also fur- 
nished information on references. I especially thank Carl 
R. Madsen and J. M. Engel, U.S. Fish and Wildlife Serv- 
ice, and James W. Grier, North Dakota State University, 
for their continued support and encouragement. Typing 
was provided by the Northern Prairie Wildlife Research 
Center. This study was supported in part by the U.S. Fish 
and Wildlife Service. 



Raptors 
Bald Eagle (Haliaeetus leucocephahis Linnaeus) 

Status: Endangered in the conterminous 48 States, except 
those populations in Washington, Oregon, Minnesota, 
Wisconsin, and Michigan where it is Threatened (U.S. 
Fish and Wildlife Service [USFWS] 1978). Primary threat 
is habitat loss; most populations appear to be recovering 
from earlier reproductive difficulties associated with 
organochlorine contamination. 

Original Discovery and Description: 

Southern bald eagle (H. I. leucocephahis Linnaeus). — 
Falco leucocephahis Linnaeus, Syst. Nat., ed. 12, vol. 1, 
1766, p. 124. Based on The Bald Eagle Aquila capite alba 
Catesby, Carolina, vol. 1, p. 1 (in America, Europa = 
South Carolina). American Ornithologists' Union [AOU] 
1957. 

Northern bald eagle (H. I. alascanus Townsend).— 
Haliaeetus leucocephalus alascanus: C. H. Townsend, 
Proc. Biol. Soc. Washington, 11, no. 34, June 9, 1897, p. 
145 (Unalaska, Aleutian Islands). AOU 1957; Mengel 
1953. 

Background: H. 1. alascanus is identical in appearance 
and slightly larger than H. I. leucocephalus. Aspects of 
reproduction, other than chronological differences 
related to climate and respective latitude, are the same. 
Formerly, 40° N latitude was arbitrarily designated as 
dividing the breeding ranges of alascanus and leuco- 
cephalus (AOU 1957; USFWS 1976). Members of both 
subspecies wander freely into the other's breeding range 
during nonbreeding periods, resulting in considerable 
confusion in identification (Dunstan 1973; Postupalsky 
1976a). As a result of these identification problems, a pro- 
posal was made to put the entire species (Haliaeetus 
leucocephalus) on the Endangered List (USFWS 1976). 
The proposal was finalized 14 February 1978 (USFWS 
1978). 

As the national emblem of the United States, the bald 
eagle plays an important part in the symbolism and cul- 
ture of our nation. As a top predator in the food chain, it 
has suffered serious declines as a result of environmental 
pollution. It also has been extirpated from large portions 
of its historic range as a result of habitat loss and human 
encroachment. 

Status Determination: The southern bald eagle was listed 
as Endangered by the U.S. Department of the Interior 
(USFWS 1973). The entire population of the bald eagle 
(H. leucocephalus) in the conterminous 48 States is now 
listed as Endangered, except for those populations in 
Washington, Oregon, Minnesota, Wisconsin, and Michi- 
gan which are listed as Threatened (USFWS 1978). 



The southern bald eagle is listed as Endangered by the 
International Union for Conservation of Nature and 
Natural Resources (1966). Godfrey (1970) lists the 
northern bald eagle as Endangered in Canada. 

Description: A large fish-eating eagle with long, broad 
wings and a large, strong bill. Adults are light to choco- 
late brown with white head and tail. Eyes, beak, legs, 
and feet are yellow. Tarsi are feathered half way to the 
feet. Immatures are brownish-black to light mottled tan 
with whitish underwing linings. Eyes are brownish and 
beak is black; legs and feet are dull yellow (Brown and 
Amadon 1968; Friedmann 1950). 

Juvenile and subadult plumages exhibit considerable 
variation; relations between the various observed 
plumages and specific age classes are not precisely known. 
Generally the body becomes lighter colored with succes- 
sive plumages until the fourth or fifth year, after which 
the typical adult plumage is attained (Southern 1964, 
1967; Brown and Amadon 1968). 

The large, bulky nests are unique and are used in lo- 
cating bald eagle territories during air and ground 
searches (Mathisen 1968r). 

See Bent (1937), Friedmann (1950), Brown and Ama- 
don (1968), Snow (1973), or birding guides for character- 
istics for identification of parts or products. 

Distribution: 

Southern bald eagle. —Historically, this species bred 
from northern California south to both coasts of Baja Cal- 
ifornia, central Arizona, New Mexico (formerly western 
Nevada and southern Utah), and from northern Texas, 
Oklahoma, Missouri (formerly Nebraska and Iowa), 
southern Illinois, western Kentucky, and Virginia south 
to the Gulf Coast and Florida. During the nonbreeding 
season (March-October) some birds wandered northward 
to northern Illinois, southern Michigan, New York, Con- 
necticut, Maine, New Brunswick, Nova Scotia, Prince 
Edward Island, and southern Quebec (AOU 1957). 

Florida remains the center of abundance with an esti- 
mated 250-300 pairs (USFWS 1973). There are a few 
nests in Louisiana and Texas, 30-50 pairs in California 
(Thelander 1973), and about 10-15 pairs in Arizona 
(Rubink and Podborny 1976). In 1973, a pair built a nest 
in Nebraska on the Missouri River, the first known 
nesting in the 1900's. The pair deserted before laying eggs 
(Lock and Schuckman 1973). See Tilt and Ruos (1976) for 
a more complete assessment of bald eagle distribution 
south of Canada. 

Northern bald eagle. — Formerly bred from Bering 
Island, the Aleutian Islands, northwestern Alaska, Mac- 
kenzie, Manitoba, central Ontario, southeastern Quebec, 
Labrador, and coasts of Newfoundland south to southern 
Oregon, Idaho, Wyoming, Colorado, South Dakota, 
Minnesota, Wisconsin, Michigan, Ohio, Pennsylvania, 
New Jersey, and Maryland. Winters from Alaska, 



northern Mackenzie, southern Ontario, Quebec, and 
southern Nova Scotia south to the southern United States 
(AOU 1957; Dunstan 1973; Postupalsky 1976a). 
Although scattered reports of nesting bald eagles in the 
middle United States exist for the 1800's and early 1900's 
they are now gone and their relationship to leucocephahis 
and alascanus is unknown. As a result, 40° N latitude has 
been selected as an arbitrary dividing line between the 
two subspecies (AOU 1957; USFWS 1976). Considering 
the lack of readily apparent differences between the two 
subspecies, even this may be superfluous (Brown and 
Amadon 1968:289). 

Centers of abundance remain in Maine, the Chesa- 
peake Bay area, Upper Peninsula of Michigan, northern 
Wisconsin, and Minnesota, northern Idaho, Oregon, 
Washington, and Alaska, Saskatchewan, Manitoba, and 
northern Ontario (Sprunt et al. 1973). Habitat loss, 
human disturbance, and environmental contaminants 
have been instrumental in declines in these areas. See Tilt 
and Ruos (1976) for a more complete assessment of bald 
eagle distribution south of Canada. 

Habitat: Bald eagle habitat is closely associated with rela- 
tively large bodies of water which provide an abundant 
source of food, primarily fish. 

In Alaska and Canada, where human disturbance is 
slight, bald eagle habitat is composed of a narrow strip of 
land along lakeshores and rivers which provide trees for 
nesting, fishing, and loafing (Hensel and Trover 1964; 
Robards and King 1966; King et al. 1972; Gerrard et al. 
1975). Human disturbance, and to some extent habitat 
loss, appear to be responsible for the considerable de- 
crease in shoreline nesting observed in more populated 
areas (Whitfield et al. 1974). The mean distance of bald 
eagle nests from water was 201 m in Canada (Gerrard et 
al. 1975) and 329 m in Alaska (Corr 1974); nests in 
Florida averaged 1.06 km from water, apparently in re- 
sponse to human disturbance (McEwan and Hirth 1979). 

Winter habitat of the bald eagle is less closely asso- 
ciated with water than summer habitat. Although most 
wintering eagles depend primarily on fish, a considerably 
wider prey base is utilized, including jack rabbits, crip- 
pled waterfowl, and carrion. Major concentrations of 
wintering bald eagles occur near wildlife refuges, dams, 
and other areas with open water (Spencer 1976). About 
half of the bald eagles wintering in the conterminous 
States occur in the Mississippi, Missouri, Wisconsin, 
Platte, and Arkansas river valleys (Steenhof 1978). Recent 
work in the western United States, including the Great 
Plains, indicates a considerable number of wintering 
eagles there (Edwards 1969; Piatt 1976; Spencer 1976). 
Communal roosting is prevalent in wintering bald eagles; 
roosts are selected primarily for protection from the wind 
(Steenhof 1978) and may be as far as 25 km from feeding 
areas (Swisher 1964). 

Decreasing numbers of large nesting trees in suitable 
nesting areas and areas that are not disturbed by human 



activities during the early stages of nesting appear to be 
the most critical aspect of habitat loss. Recreational use of 
lakes and extensive shoreline development have reduced 
feeding habitat. Acid rain threatens to reduce lake 
fisheries. Lakes with high sensitivity to acid rain are gen- 
erally found in northern California, Oregon, Washing- 
ton, northern Idaho, Montana, northeastern Minnesota, 
northern Wisconsin and Michigan, and east of the Appa- 
lachians (U.S. Environmental Protection Agency 1979). 

Feeding Habits: Bald eagles are primarily fish eaters; 
however, they are opportunistic and will utilize avian 
and mammalian prey and carrion if readily available, 
especially in the nonbreeding season (Herrick 1934; Bent 
1937; Murie 1940; Broley 1952; Tate and Postupalsky 
1965; Southern 1966; Retfalvi 1970; Hehnke 1973; Dun- 
stan and Harper 1975; Ofelt 1975). In some coastal areas, 
birds and reptiles form an important part of the diet 
(Ogden 1975; personal observation in Maine). 

The birds usually hunt from perches adjacent to water 
but they also hunt while in flight. Live, dying, or dead 
fish are taken from the water with the feet or from shal- 
low water with the beak and carried to the nest or a 
feeding perch. Fish or other prey too heavy to lift are 
dragged to shore with a heavy rowing motion of the 
wings (Campbell 1969; Edscorn 1973). Occasionally fish 
are purloined from hapless ospreys or other fish-eating 
birds (Brown and Amadon 1968; Grubb 1971; Ogden 
1975). 

The diet varies considerably with geographic area and 
season. Wintering northern bald eagles utilize a much 
wider prey base (Southern 1963, 1964; Piatt 1976; 
Spencer 1976). Little is known about food habits of non- 
breeding southern bald eagles. 

In captive breeding experiments whole fish and a 
variety of whole animals (e.g., chickens, rats, mice) were 
fed; a diet partially consisting of a commercial food (Zu- 
preem and Nebraska Brand Birds of Prey Diet) has been 
used during the nonbreeding season (Maestrelli and 
Wiemeyer 1975; see Appendix). 

Reproduction and Development: Eagle nests are charac- 
teristically large, ranging from a minimum of 1 m in 
width and depth to 5 m deep and 3 m across; size and 
shape are determined partly by the supporting branches. 
Nests are usually in live trees, the species depending on its 
propensity for large, strong branches or forks for nest sup- 
port, and height above the canopy (Mathisen 1969a; 
Frenzel et al. in Madsen 1973; Gerrard et al. 1975). In 
the Aleutians, coastal areas, Arizona, and other regions 
where suitable nest trees are scarce, nests are placed on 
ridges, cliffs, and on seastacks (Troyer and Hensel 1965; 
Sherrod and White 1975; Rubink and Podborny 1976). 
Ground-nesting has been recorded on an island near Yel- 
lowknife, Northwest Territories (Bromley and Trauger 
1974). 

Initiation of egg-laying appears to vary with tempera- 



ture, which in turn generally varies with latitude, begin- 
ning as early as November and continuing through mid- 
January in Florida (Broley 1947). In Arizona incubation 
was first observed on 14 February (Rubink and Podborny 
1976). In Wisconsin, the earliest estimated egg-laying oc- 
curred in late February; most clutches are completed by 
1 April (C. R. Sindelar, Jr., personal communication). 
The Aleutians and Pacific Coast are warmed by the 
Davidson and "Japanese" currents (Nelson and Myres 
1975) and breeding is initiated considerably earlier than 
at corresponding latitudes in the interior (Retfalvi 1965; 
Sherrod and White 1975). 

Bald eagles engage in courtship flights consisting of the 
pair soaring together for long periods of time at great 
heights. Occasionally they will lock talons and somersault 
downward several hundred feet (Brown and Amadon 
1968). Two or three eggs are typically laid, although 
four-egg clutches have been recorded (Herrick 1932). In- 
cubation lasts about 35 days (Herrick 1934). 

Newly hatched young are covered with white or gray 
down which is replaced by thicker gray down at 2-3 
weeks; first feathers appear at 4-5 weeks. Fledging occurs 
at 10-12 weeks and the young are dependent upon the 
parents for several more weeks (Brown and Amadon 
1968). Frenzel (in Madsen 1973:29) stated that about 
80% of fledgling eagles in their Minnesota study spent 
some time on the ground before becoming proficient at 
flying. They appeared to be fed normally by the parents 
even though they were on the ground. 

Bald eagles are believed to reach sexual maturity at 5 or 
6 years of age (Sherrod et al. 1976). Little is known about 
longevity and length of sexual activity; however, a dead 
bald eagle was recently recovered on an island in western 
Lake Erie that was 27 years old. (L. Van Camp, personal 
communication). Captive bald eagles have reached 50 
years of age (Snow 1973). Sherrod et al. (1976) estimated 
adult mortality at 5.4 % per year and a collective mortal- 
ity of subadult birds before breeding age to be 90% or 
more on Amchitka Island, Alaska. 

Diseases and Parasites: A variety of diseases and parasites 
have been reported in the bald eagle, including avian 
cholera (Locke et al. 1972; Rosen 1972), aspergillosis 
(Coon and Locke 1968), and an enteric bacterial patho- 
gen, Edwardsiella tarda (White et al. 1973), infestations 
of helminth parasites (Kocan and Locke 1974), and others 
(Coon et al. 1970). None occur frequently nor are con- 
sidered limiting factors. 

Predators and Other Mortality Factors: Occasionally rac- 
coons, bobcats, crows, and under unusual circumstances 
gulls, prey on eggs and small young, forcing the adults 
away from the nest (see Fyfe and Olendorff 1976). 

Severe weather may have serious effects on reproduc- 
tion. The Florida hurricane in October 1944 resulted in 
widespread nesting failures in the subsequent breeding 
season (Broley 1947). Severe storms, especially in the 



North, may result in temporary nest abandonment, caus- 
ing destruction of eggs or young. 

Persistent pesticides also lower productivity. The rela- 
tion between organochlorines (notably DDE) and egg- 
shell thinning is now well established (Hickey and Ander- 
son 1968; Hickey 1969; Krantz et al. 1970; Wiemeyer et 
al. 1972). DDE interferes with normal calcium metabo- 
lism, resulting in thin-shelled eggs which cannot with- 
stand normal incubation. Populations reaching 17-20% 
eggshell thinning exhibit severe reproductive difficulties 
and resulting declines (Anderson and Hickey 1972). Diel- 
drin, PCB's, and mercury have been linked to embryonic 
and early chick mortality (Anonymous 1970; Wiemeyer 
et al. 1972). High concentrations of dieldrin and DDT are 
known to result in outright deaths of bald eagles (Chura 
and Stewart 1967). Of 153 eagles analyzed between 1964 
and 1970 almost 10% of the deaths were attributed to 
dieldrin poisoning (Belisle et al. 1972). 

Illegal shooting remains the greatest single known 
source of bald eagle mortality. Roughly half of all re- 
corded bald eagle deaths are a direct result of shooting. 
Other causes of mortality include impact injuries (usually 
with powerlines or towers), electrocution, trapping in- 
juries (eagles caught in "sight bait" sets for furbearers), 
automobile or train accidents, and poisoning from con- 
taminated coyotes or other carcasses (Coon et al. 1970; 
Mulhern et al. 1970; Belisle et al. 1972; Sprunt 1972). 

Population Level: 

Southern bald eagle. — Reduced populations in Florida 
due to loss of habitat and effects of DDE. Current repro- 
duction appears adequate for maintenance of the remain- 
ing population, although productivity in southern 
Florida is lower than in central and northern Florida 
(Nesbitt et al. 1975). Populations on the Georgia-Caro- 
lina coast, Gulf Coast, Arizona, and lower California 
have decreased significantly and are suffering low repro- 
ductivity (Tilt and Ruos 1976). 

Northern bald eagle. — Alaskan populations, estimated 
at 35,000 to 40,000 nesting pairs, appear to be doing 
well. In the conterminous 48 States, substantial reduction 
of populations occurred before 1950, primarily due to 
human disturbance and habitat loss. Since then, pesticide 
contamination has further reduced populations, 
especially those in coastal areas and on the Great Lakes 
shores. Populations nesting on interior lakes west of Lake 
Erie appear to be reproducing at an adequate rate and 
may be increasing slowly (Postupalsky 1978b; C. R. 
Sindelar, personal communication). Populations east of 
western Lake Erie are experiencing poor reproduction, 
especially in northern Ohio. Maine appears to have very 
poor reproduction as a result of spruce budworm control 
programs and is currently one of the most endangered 
populations. However, reproduction in 1976 showed a 
slight upturn (Tilt and Ruos 1976). 

Thacker (1971) estimated that over 130 bald eagles are 
held for research purposes and by zoos. Captive propaga- 



tion at the Patuxent Wildlife Research Center, Laurel, 
Maryland, resulted in 12 young raised from 1973 to 1977 
plus 1 young raised from three captive-produced eggs 
placed in eagle nests in the wild in 1977. It appears tech- 
nically possible to augment wild populations with cap- 
tive-produced offspring (Maestrelli and Wiemeyer 1975; 
S. Wiemeyer, personal communication). 

Reasons for Current Status: Conversion of habitat to agri- 
cultural and industrial uses, habitat loss from logging, 
recreational utilization of lakes and lakeshores and con- 
comitant human disturbance have effected a slow, long- 
term decline that began not long after the arrival of white 
men on the continent. These declines were probably ac- 
celerated in the late 1800's and early 1900's during the 
heyday of lumbering. Recent emphasis on recreational 
development represents an increasing threat to bald eagle 
habitat (Sprunt 1969; Weekes 1975a). 

Illegal shooting remains the single most frequent cause 
of death of recovered bald eagles even though they are 
completely protected by the Bald Eagle Protection Act 
(16 USC 668-668d). Habitat protective provisions were 
extended to the northern bald eagle upon enactment of 
the proposal to place the entire species on the Endangered 
List. 

Recent large-scale declines in reproduction have re- 
sulted from biocide pollutants, notably DDE. The most 
vulnerable populations are those nesting on the shores of 
the Great Lakes and in the northeastern United States. All 
populations, except in Alaska, appear to have suffered de- 
clines from environmental contaminants; the magnitude 
in any one area appears to be relative to the contaminant 
level in that area. The Florida population appears to be 
midway in the spectrum of productivity of bald eagles, 
whereas Wisconsin interior lakes and Alaska are among 
the highest and Maine and the Great Lakes shores are the 
lowest (Sprunt et al. 1973). 

Recovery Team: Information concerning recovery teams 
and recovery plans in progress may be obtained from the 
Office of Endangered Species, U.S. Fish and Wildlife 
Service, 1000 Glebe Road, Arlington, VA 22203. 

Management Activities: Specific habitat management 
plans are being used on U.S. Forest Service lands and by 
various States. Cooperative agreements with landowners 
of nesting territories are being implemented by the 
Florida Audubon Society and in Wisconsin and Maine 
(USFWS 1973; Madsen 1973; U.S. Forest Service 
Manual, Tide 2600, Wildlife Management). 

Modification of powerlines to substantially decrease 
electrocution is being carried out, especially in the 
western States where electrocution is a greater mortality 
factor than in the East (Marshall 1940; U.S. Department 
of Agriculture 1972; Miller et al. 1975). 

Cooperative efforts between Federal, State, and 
private individuals are under way to assess yearly produc- 



tion and status of bald eagles. Additional studies are being 
done on food habits, post-fledgling movements, and win- 
tering (see bibliography for specific studies). The 
National Wildlife Federation is compiling a bald eagle 
data bank on research efforts around the country. 

Bald eagles are protected by the Bald Eagle Protection 
Act of 1940 and by the Endangered Species Act of 1973. 
Public information programs, notably a promotional 
public relations program sponsored by the Chippewa Na- 
tional Forest (Minnesota) and Hunt & Wesson Foods to 
buy bald eagle habitat, have been very successful 
(Mathisen in Madsen 1973:43-44). Eagle Valley Environ- 
mentalists, P.O. Box 155, Apple River, Illinois 61001, 
sponsor an annual meeting of bald eagle researchers and 
the public. Topics cover a wide range of bald eagle biol- 
ogy and focus on winter ecology. 

Migration counts are maintained at various hawk- 
watches around the country (see Newsletter of Hawk Mi- 
gration Association of North America). The Raptor Infor- 
mation Center of the National Wildlife Federation con- 
ducts an annual midwinter bald eagle census in coopera- 
tion with the U.S. Fish and Wildlife Service. 

From 1977 through 1979, 18 captive-produced young 
from the Patuxent Wildlife Research Center fledged in 
the wild, introduced by a variety of techniques including 
transplanting young to active nests and hacking young at 
artificial platforms. Eggs suspected of being thin-shelled 
were collected during these operations and were incu- 
bated at Patuxent; four hatched and the young were re- 
turned to active nests in the wild (S. N. Wiemeyer, per- 
sonal communication). New York has been foremost in 
reintroduction research involving hacking young at arti- 
ficial sites. Since 1976, all 15 young released fledged suc- 
cessfully and several birds returned to the area in subse- 
quent years (P. Nye, personal communication). 



References and Selected Bibliography 

Abbott.J.M. 1959. Bald eaglesurvey report. Atl. Nat. 14(4):252- 
258. 

Abbott, J. M. 1963. Bald eagle survey for Chesapeake Bay, 1962. 
Atl. Nat. 18(l):22-27. 

Abbott, J. M. 1964. Bald eagle survey for the Chesapeake Bay re- 
gion. Atl. Nat. 19(4):233-236. 

Abbott. J. M. 1967. The Chesapeake bald eagles: summary re- 
port- 1936; 1955-1965. Atl. Nat. 22(l):20-25. 

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13 



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Burrowing Owl (Athene cunicularia Molina) 



Status: 

Western burrowing owl. — Severe declines, especially 
those populations dependent upon prairie dogs and other 
persecuted small mammals for nesting burrows. 

Florida burrowing owl. —Increasing. 

Original Discovery and Description: 

Western burrowing owl (Athene cunicularia hypu- 
gaea Bonaparte) .— Strix hypugaea Bonaparte, Am. 
Ornithol. vol. 1, 1825, p. 72 (note). (Western United 
States — Plains of the Platte River.) American Ornitholo- 
gists' Union 1957. 

Florida burrowing owl (Athene cunicularia floridana 
Ridgway). — Speotyto cunicularia var. floridana Ridg- 
way, Am. Sportsman, 4, no. 14 (n.s. no. 40), July 4, 
1874, p. 216. (16 miles east of Sarasota Bay, Manatee 
County, Florida.) AOU 1957. 

Background: Although the Florida burrowing owl and 
the western burrowing owl are somewhat similar in ap- 
pearance, the wide separation of their ranges makes con- 
fusion unlikely. In 1976, the burrowing owl was placed in 
the genus Athene (AOU 1976). It formerly was placed in 
a separate genus Speotyto. 

The burrowing owl is a small diurnal, crepuscular, and 
nocturnal owl, unique in its underground semicolonial 
nesting behavior. 

Status Determination: Listed as "Status — Undetermined" 
by the U.S. Fish and Wildlife Service (1973). Has been on 
the Blue List, an "early warning" list of species exhibiting 
potentially serious declines, since 1971 (see December 
issues of American Birds, 1971 to present). 

Description: A small owl with relatively long legs and a 
short stubby tail. Adults are brown above with buff to 
buffy white spots, underparts buffy barred narrowly with 
dark brown. Juveniles are similar to adults, unstreaked to 
moderately streaked and light to brownish buff below, 
and have a wing stripe (buffy as opposed to the brown 
middle secondary coverts of adults). Adult plumage is at- 
tained in August or September. Florida burrowing owls 
tend to be darker in color overall than the western bur- 
rowing owl (W. D. Courser, personal communication). 
Burrowing owls are somewhat atypical among raptors 
in that they do not exhibit reverse size dimorphism; males 



14 



average slightly larger than females. Identification of sex 
of adults is usually possible during the breeding season. 
Males have less barring on the breast and usually have 
faded plumage from being in the sun more than the incu- 
bating females; males are light gray-brown and females 
darker chocolate brown. Plumage color differences disap- 
pear after the postnuptial molt in late summer. Behav- 
ioral differences (i.e., female remaining very close to the 
nest burrow and males conspicuously hunting and pro- 
viding food) aid sexing of breeding pairs. Solitary owls 
are often difficult to sex (Butts 1973; Thomsen 1971). 

The presence of debris, cow or horse dung, droppings, 
molted feathers, and owl pellets containing primarily in- 
sect remains at the mouth of a burrow indicate nesting ac- 
tivity (Butts 1973). In urban situations, grass divots and 
other material replace dung as nesting material. 

See Bent (1938), Grossman and Hamlet (1964), and 
birding guides for characteristics for identification of 
parts of products. 

Distribution: Breeds in prairie regions west of a line from 
northwestern Louisiana north to western Manitoba. Win- 
ters in the southern parts of its range south to western 
Panama (Butts 1973; AOU 1957). The Florida burrowing 
owl is resident, occupying the prairies of central and 
southern Florida; the prehistoric range, however, was ap- 
parently somewhat greater (Ligon 1963; AOU 1957). 

Bange discontinuities probably have been widened by 
extensive prairie dog extermination on the Great Plains 
(Butts 1973). The population in Florida expanded as land 
was cleared for the cattle industry (Ligon 1963); burrow- 
ing owls are now within 48 km of the Georgia border and 
are breeding on the Florida Keys (Courser 1976a, 1979). 

Habitat: Burrowing owls inhabit non-forested plains, 
grasslands, and deserts (Butts 1973). Urban environments 
meeting habitat requirements may be utilized (Thomsen 
1971; Coulombe 1971). They are largely "dependent 
upon various digging mammals for nesting burrows" 
(Thomsen 1971) in the West. 

Burrows play a dominant role in the ecology of the bur- 
rowing owl. In addition to nesting, they are used 
throughout the year for roosting and escape. Burrows of 
prairie dogs, various species of ground squirrels and kan- 
garoo rats (depending on local abundance), and, occa- 
sionally, abandoned burrows of badger, coyote, and swift 
fox may be used. Digging of their own burrows appears to 
be infrequent in the West (Butts 1973; Thomsen 1971; 
Martin 1973fc). In Florida up to 60% of the burrows are 
dug by the owls; gopher turtle holes are the other main 
source of burrows used (W. D. Courser, personal com- 
municaton). Burrows utilized by owls are invariably in 
areas of short vegetation (Butts 1973; Thomsen 1971). 
Nesting burrows typically slant downward at a 15° 
angle and usually have a turn within 1 m (Butts 1973). 

When the young owlets (about 2 weeks old) come to the 
mouth of the burrow they use nearby auxiliary burrows 



and usually use two or three different burrows in succes- 
sion before they fledge. After fledging they occupy indi- 
vidual burrows at random in the vicinity. Owls in the 
northern parts of their winter range are primarily noc- 
turnal, as opposed to diurnal and crepuscular in the sum- 
mer, and spend the daytime in burrows (Butts 1976). In 
Florida and the southern parts of the winter range, owls 
can usually be seen during the daytime (W. D. Courser, 
personal communication). 

Critical Habitat: Poisoning of prairie dog towns, with 
which colonies of western burrowing owls are often asso- 
ciated, substantially reduces burrowing owl populations. 
Burrow habitat in abandoned prairie dog towns becomes 
unsuitable for burrowing owls within 1-3 years (Butts 
1973). 

Feeding Habits: Feeds primarily on arthropods and small 
mammals. Small reptiles, amphibians, and birds are in- 
frequent in the diet. Invertebrate forms, when available, 
are most frequently taken, although in some areas the diet 
appears to be more varied (Longhurst 1942; Best 1969; 
Coulombe 1971; Thomsen 1971; Butts 1973; Smith and 
Murphy 1973£>; W. D. Courser, personal communica- 
tion). 

Ground foraging, in a manner similar to robins, occurs 
most frequently. Foraging from observation perches and 
from a hovering position also occurs extensively. Fly- 
catching behavior has been noted infrequently (Thomsen 
1971; Butts 1973). W. D. Courser (personal communica- 
tion) observed owls feeding on insects attracted to lighted 
areas. 

In the summer arthropods are very prominent in the 
diet. Small mammals are eaten more frequently in the 
winter in the United States. In the summer, burrowing 
owls are primarily diurnal but become essentially noc- 
turnal in the winter months (Butts 1973). Owls wintering 
in central America are likely to have arthropod prey 
available and may retain diurnal feeding schedules. 

Reproduction and Development: Courtship and pair 
formation occur in March and April in most areas (Grant 
1965; Best 1969; Butts 1973) but may begin as early as 
late December in California (Thomsen 1971) and Florida 
(W. D. Courser, personal communication). Burrow selec- 
tion occurs primarily at dusk and during the night 
(Thomsen 1971). Nesting material, consisting primarily 
of organic debris and dried manure of cattle, horse, or 
other species, is carried to the burrow entrance; litter is 
often used as nesting material in areas of human inhabita- 
tion (W. D. Courser, personal communication). Dirt and 
debris are scraped out of the burrow with the feet; oc- 
casionally the beak and wings are also used. The tunnel is 
usually 18-22 cm wide by 15-19 cm high with a larger 
nest chamber at the end. Owl-dug burrows in Florida are 
15-20 cm wide by 10-13 cm high (W. D. Courser, 
personal communication). When the nesting burrow has 



15 



been suitably modified, the nesting material is distributed 
throughout the burrow (Walker 1952; Thomsen 1971; 
Butts 1973). 

Pair formation is initiated by unpaired males (Thom- 
sen 1971). Paired birds engage in ritualistic behavior, dis- 
playing white facial and throat patches, leading to copu- 
lation, which occurs most frequently at dusk and after 
dark (Martin 1973&; W. D. Courser, personal communi- 
cation). Nest site selection begins after pair formation; the 
males gather and distribute most of the nesting material. 
Average clutch size is 6.48 for both subspecies (Murray 
1976). One brood is raised per year; renesting will occur 
if the clutch is destroyed early in incubation. Incubation, 
which lasts 28-29 days, is done entirely by the female 
(Coulombe 1971; Thomsen 1971). The male provides all 
food during incubation and the early nestling stage. The 
female assists in foraging when the young reach 3-4 
weeks of age (Martin 1973£>). Most feeding occurs at 
dawn and dusk, continuing until midnight (Grant 1965, 
Thomsen 1971; W. D. Courser, personal communica- 
tion). 

When hatched, the young are covered with white, 
fuzzy down. They begin feathering out at 2 weeks, when 
they are also first observed at the burrow entrance. The 
young run and forage by 4 weeks of age and are capable 
of sustained flight by 6 weeks (Butts 1973). Owl families 
often switch burrows every 10-15 days when the young 
are 3^4 weeks old (Butts 1973) and remain as a loose-knit 
group until early fall when the young begin to disperse to 
nearby burrows (Thomsen 1971). 

Burrowing owls begin breeding when 1 year old 
(Thomsen 1971; K. O. Butts, personal communication). 
Life span is uncertain; the oldest recorded age is 8 years 
and 8 months (Kennard 1975). 

Diseases and Parasites: Fleas, lice, and ants are occa- 
sionally found on birds or in burrows; related mortality 
appears to be insignificant (Thomsen 1971). Examination 
of about 30 birds failed to reveal any indication of blood 
parasites (see Greiner and Kocan 1977; W. D. Courser, 
personal communication). 

Predators and Other Mortality Factors: Badgers, coyotes, 
domestic dogs and cats, snakes, and bobcats are the most 
important predators of eggs and young owlets (Butts 
1973; Martin 1973&). Older nestlings and adults may be 
taken by large raptors (Martin 1973fo). 

Shooting and roadway mortality are most important 
for owls over seven weeks old (Butts 1973). Food may be a 
limiting factor during brood rearing (Thomsen 1971; 
Butts 1973). Because of the relatively low position of the 
burrowing owl on the food chain, pesticide-related repro- 
ductive difficulties are probably insignificant. Poison- 
related deaths, especially in areas of prairie dog extermi- 
nation, may be an important mortality factor (Butts 
1973). Nesting failure may be caused by flash flooding, 
burrow destruction by agricultural operations, and fumi- 



gation and sealing of the burrow (Butts 1973). Persecu- 
tion by ranchers has been a problem in Florida (Nicholson 
1954).' 

Population Level: Estimates of the current burrowing 
owl population are lacking, other than on relatively re- 
stricted study areas (Coulombe 1971; Thomsen 1971; 
Butts 1973). Substantial declines have coincided with ex- 
tensive extermination of burrowing rodents, especially 
prairie dogs, with which burrowing owls are intimately 
associated (Butts 1973). In areas where burrowing owls 
are associated with less persecuted species, they do not ap- 
pear to be declining (Thomsen 1971). The Florida popu- 
lation is expanding in conjunction with land cleared for 
the cattle industry and is roughly estimated at about 
1,000 pairs (W. D. Courser, personal communication). 

Thacker (1971) estimated roughly 77 burrowing owls 
held by zoos or for research. 

Reasons for Current Status: The primary factor attribut- 
able to burrowing owl declines is the widespread elimina- 
tion of burrowing rodents, notably prairie dogs and var- 
ious species of ground squirrels. As an example, prairie 
dog towns in Oklahoma declined from millions of acres in 
historic times to just 9,522 acres in 1968. Prairie dog 
towns poisoned during Butts' (1973) study showed an es- 
sentially complete elimination of burrowing owls, as bur- 
rows became unsuitable for owls within 1-3 years even in 
the absence of cultivation. 

Illegal shooting may be responsible for substantial mor- 
tality in some areas, accounting for 10 of 15 deaths in one 
study (Butts 1973). Other studies, however, did not men- 
tion shooting as a source of mortality (Coulombe 1971; 
Thomsen 1971; Martin 1973fo). 

Management Activities: Butts (1973) suggests establishing 
"refuge" prairie dog towns in areas where poisoning is 
widespread, and limiting poisoning operations with 
treated grain to January and February' (in areas where 
most owls migrate from the breeding range). 

Collins and Landry (1977) described artificial nesting 
burrows that were widely accepted. This new technique 
may prove valuable for preservation and rehabilitation of 
existing range, and possibly for reintroduction to former 
range. 

Burrowing owls are protected by the United States- 
Mexico Migratory Bird Treaty of 10 March 1972. 

Little emphasis is placed on breeding burrowing owls 
at this time. 



References and Selected Bibliography 

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Agersborg, G. S. 1885. The birds of southwestern Dakota. Auk 
2(3):276-289. 

Alcorn, G. D. 1941. The western burrowing owl in Grays Har- 
bor County, Washington. Murrelet 22(3):57-58. 



16 



Allen, A. F. 1914. Burrowing owl breeding in Iowa. Wilson 
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American Ornithologists' Union. 1957. Check-list of North 
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American Ornithologists' Union. 1976. Thirty-third supplement 
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Anderson, J. W. 1978. A method to reintroduce burrowing owls 
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Bent, A. C. 1938. Life histories of North American birds of prey. 
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Berdan, C. A., and R. L. Linder. 1973. Burrowing owls in Mel- 
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Berger, R. ]., and J. M. Walker. 1972. Sleep in the burrowing 
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Best, T. R. 1969. Habitat, annual cycle, and food of burrowing 
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Bond, J. 1943. Florida burrowing owl in Cuba. Auk 60(1):105. 

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Brenckle, J. F. 1936. The migration of the western burrowing 
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Burton, J. A., ed. 1973. Owls of the world, their evolution, 
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Buscher, H. N. 1978. Echinoparyphium speotyto Sp. N. (Trema- 
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Butts, K. O. 1971. Observations on the ecology of burrowing 
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Butts, K. O. 1973. Life history and habitat requirements of bur- 
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Collins, C. T. 1976. Food-caching behavior in owls. Raptor Res. 
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Collins, C. T., and R. E. Landry. 1977. Artificial nest burrows 
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Coulombe, H. N. 1968. Energy exchange in the biology of the 
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fornia, Los Angeles. 180 pp. 



Coulombe, H. N. 1970. Physiological and physical aspects of 
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chem. Physiol. 35(2):307-337. 

Coulombe, H. N. 1971. Behavior and population ecology of the 
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Courser, W. D. 1972. Variability of tail molt in the burrowing 
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Greiner, E. C, and A. A. Kocan. 1977. Leucocytozoon (Haemo- 
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17 



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four owls in north-central Colorado. Southwest. Nat. 14(2): 
163-170. 

Marti, C. D. 1970. Feeding ecology of four sympatric owls in 
Colorado. Ph.D. Thesis. Colorado State University, Fort Col- 
lins. 119 pp. 

Marti, C. D. 1973. Food consumption and pellet formation rates 
in four owl species. Wilson Bull. 85(2): 178-181. 

Marti, C. D. 1974. Feeding ecology of four svmpatric owls. Con- 
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Martin, D. J. 1971a. A trapping technique for burrowing owls. 
Bird-Banding 42(1):46. 

Martin, D. J. 1971b. Unique burrowing owl pellets. Bird-Band- 
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Martin, D. J. 1973a. A spectrographic analysis of burrowing owl 
vocalizations. Auk 90(3):564-578. 

Martin, D. J. 1973b. Selected aspects of burrowing owl ecology 
and behavior. Condor 75(4):446-456. 

Maser, C, E. W. Hammer, and S. H. Anderson. 1971. Food 
habits of the burrowing owl in central Oregon. Northwest 
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McBee, C. E. 1927. Notes on the food of the burrowing owl. 
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McClure, H. E. 1951. An analysis of animal victims on Nebras- 
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Murray, G. A. 1976. Geographic variation in the clutch sizes of 
seven owl species. Auk 93(3):602-613. 

Neff, J. A. 1941. A note on the food of burrowing owls. Condor 
43(4): 197-198. 

Neills, W. T. 1954. Notes on the Florida burrowing owl. Fla. 
Nat. 27(3): 67-70. 

Nicholson, D. J. 1954. The Florida burrowing owl. a vanishing 
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Olendorff, R. R. 1973. The ecology of the nesting birds of prey of 
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53. 

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14. 

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Powers, A. L., and P. L. Mcintosh. 1975. The burrowing owl 
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Probst, F. M. 1978. Burrowing owl photographed at Huntington 
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ll(3):62-66. 

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dangered species. Burrowing Owl. U.S. Bur. Land Manage.. 
Tech. Note 11. 25 pp. 



Caracara (Caracara cheriiray Jacquin) 

Status: Peripheral — Rare; declines in the United States 
are thought to be related to habitat loss. 

Original Discovery and Description: Caracara cheriway 
audubonii: Puhjboru.s auduhonii Cassin, Proc. Acad. Nat. 



18 



Sci. Philadelphia, 17, no. 1., Jan.-Mar. (Aug. 7), 1865, 
p. 2 (Florida). American Ornithologists' Union 1957. 
Listed as Polyborus plancits in Brown and Amadon (1968) 
and as Polyborus cheriway audubonii in Friedmann 
(1950). 

Background: The caracara is a specialized carrion-eating 
hawk of open or semi-open country and spends much of 
its time on the ground scavenging. Its distribution is 
limited to the extreme southern United States, continuing 
south through Mexico, where it becomes common. It is 
the national bird of Mexico and is called the Mexican 
eagle there (Brown and Amadon 1968). The Guadalupe 
caracara (Caracara lutosa) inhabited Guadalupe Island 
and Baja California. Now extinct; was last reported in 
1903 (AOU 1957, 1973). 

Status Determination: Listed as Status Undetermined by 
the U.S. Fish and Wildlife Service (1973). Has been on 
the Blue List, an "early warning" list of species exhibiting 
potentially serious declines, since 1971 (see December 
issues of American Birds, 1971 to present). 

C. c. audubonii in Florida is listed as threatened by the 
Florida Commission on Bare and Endangered Plants and 
Animals and the Florida Game and Fresh Water Fish 
Commission. 

Description: A large caracara with a crest, elongate neck, 
large hooked beak, and long legs. Sides of head and chin 
bare with scattered bristles. Bill is whitish becoming 
bluish at the base. Eyes are brown. Wingspread is about 
120 cm (Brown and Amadon 1968). Adults are blackish 
on the crown, wings, lower back, and upper abdomen. 
The lower part of the head, throat, lower abdomen, and 
under tail coverts are white, sometimes tinged with yel- 
low; breast and upper back whitish, heavily barred with 
black. Tail is white with narrow dark bars and a broad 
subterminal band. Prominent white wing patches are re- 
vealed in flight. Facial skin is reddish, and turns yellow 
when excited. Legs are yellow (Layne 1976). Color pat- 
tern of juveniles is similar, but is brownish and buffy; the 
breast and upper back are streaked instead of barred. 
Facial skin is pinkish, turning gray when excited. Legs 
are gray (Layne 1976). 

Wing chord of males 360-382 mm, tail 186-203 mm; 
wing chord of females 382-400 mm, tail 202-228 mm 
(Oberholser 1974). 

See Friedmann (1950), Brown and Amadon (1968), 
Oberholser (1974), and birding guides for characteristics 
for identification of parts or products. 

Distribution: Baja California, southern Arizona, New 
Mexico, and Texas south through Mexico. Central 
Florida south to Cuba and the Isle of Pines (AOU 1957). 
Arizona. — Besident in small numbers on the Papago 
Indian Beservation, casual east to Santa Cruz Valley, 
west to Gila Bend and extreme southeastern Yuma 



County. Old records extend to Santa Cruz and Salt River 
valleys, Oracle, and Yuma (Phillips et al. 1964). 

New M exico. — Extremely rare in New Mexico. Peri- 
odic presence may be confined to the Rio Grande Valley, 
also has occurred in southwestern New Mexico (Ligon 
1961). 

Texas. — Fairly common to uncommon in south Texas 
brush country and on coast north to about 29°N; uncom- 
mon to scarce and somewhat irregular in central portions 
from San Antonio and Gonzales north to Waco and Na- 
varro County, scarce and irregular northwest to Johnson 
County and on the upper coast. Formerly bred on 
Edwards Plateau, eastern Concho County. May have 
bred in Brewster County, 10 miles north of Terlingua. 
Wanders northward irregularly to Coleman, Baylor, and 
Grayson counties; casual straggler to northern Panhandle 
and eastern Trans Pecos (Oberholser 1974). 

Louisiana. — Decidedly rare permanent resident, one 
or two pairs nesting in Cameron Parish, where the major- 
ity of sightings have been reported (Lowery 1974). 

Florida. —The bulk of the population is in the south- 
central prairie region. Casual records in recent years from 
as far north as Alachum (Gainesville), Duval (Jackson- 
ville), and Nassau (Fernondiva) counties and as far south 
as the lower Florida keys (Monroe County). Preliminary 
analysis of a survey covering 1973-76 gives a minimum 
estimate of the population of about 350-400 individuals 
(J. N. Layne, personal communication). 

Habitat: The caracara inhabits arid prairies and grass- 
lands, and open desert brushland, usually at lower eleva- 
tions (Brown and Amadon 1968; Oberholser 1974). 

Caracaras are known to nest in clumps of live oak, 
cacti, and in cabbage palms in Florida (Brown and Ama- 
don 1968). Porter and White (1977) reported that de- 
clines may be related to clearing of chaparral brushlands. 

Little is known, but there appear to be no major sea- 
sonal or stage of life cycle differences in habitat use 
(Brown and Amadon 1968; Oberholser 1974). 

Critical Habitat: Declines in some areas are thought to be 
associated with habitat loss resulting from clearing of 
chaparral brushlands (Porter and White 1977). 

Feeding Habits: The caracara is both a scavenger and a 
predator. It spends much time on the ground searching 
for insects, grubs, and worms, and pursues reptiles, am- 
phibians, birds, and small mammals. Also robs bird nests 
and may force other birds (raptors, gulls, pelicans) to give 
up their food. Often feeds on carrion, although it is 
thought to be more interested in the associated insect 
larvae (Glazener 1964; Grossman and Hamlet 1964; 
Brown and Amadon 1968; Batten 1969; Oberholser 
1974). 

Flies at moderate altitude searching for carrion or 
prey. Also flies close to the ground, similar to marsh 
hawks. Spends much time on the ground searching for 



19 



prey (Oberholser 1974). 

Larger groups of up to 10 birds are seen in the non- 
breeding season. This may be associated with carrion 
feeding habits (Oberholser 1974). 

Reproduction and Development: Caracaras typically be- 
gin breeding in December to February in Florida and 
slightly later in the western United States (Brown and 
Amadon 1968; Batten 1969). Nests have been found in 
cabbage palms in Texas (Smith 1910) and in Florida 
(Brown and Amadon 1968), elsewhere in low bushes or 
trees 1.5-15.3 m high (Oberholser 1974). The nest, 
which is often reused, is made of sticks and sometimes 
lined with dry dung, trash, or pieces of hide or bone 
(Brown and Amadon 1968; Batten 1969). 

Little is known about courtship behavior. Batten 
(1969) stated that they utter a cackling call during the 
breeding season during which the head is thrown back, 
nearly touching the shoulders. Males sometimes fight in 
the air (Brown and Amadon 1968). Two or three eggs, 
rarely four, are laid. Both parents take part in incuba- 
tion, which is about 30 days (Layne 1976). There is some 
evidence that two broods are occasionally raised (Brown 
and Amadon 1968). The fledgling period lasts about 
2 months, during which the young are fed primarily fresh 
meat by both parents (Brown and Amadon 1968; Batten 
1969). 

Brown and Amadon (1968:133) reported a caracara in 
captivity over 30 years old. 

Predators and Other Mortality Factors: Detailed studies 
on natural predators are lacking. Pesticide contamination 
is not known to be a factor; food habits of caracaras do 
not indicate that they would be affected by organo- 
chlorine-induced eggshell thinning. In some livestock- 
producing areas in South America, caracaras attack 
young lambs and are severely persecuted (Grossman and 
Hamlet 1964). Layne (1976) also reported persecution of 
caracaras in Florida for supposed predation of young live- 
stock. In earlier years, large numbers of caracaras were 
apparently destroyed in vulture trapping operations in 
Florida (Layne 1976). 

Population Level: 

Arizona. — Probably never was common (Phillips et al. 
1964). Nested in small numbers on the Papago Indian 
Reservation, where the last known nesting records for 
Arizona occurred in 1960 (Levy 1961; Porter and White 
1977). 

New Mexico. — Extremely rare. One known nesting oc- 
curred in 1953, in the Rio Grande Valley at Bellen, south 
of Albuquerque (Ligon 1961). 

Texas. — Fairly common to uncommon in the south 
Texas brush country. Populations appear to have declined 
substantially in the last two decades. On the Welder 
Wildlife Refuge breeding pairs have declined from 35 in 
the 1950's to 1 or 2 pairs in 1978 (Porter and White 1977). 



The largest annual Christmas Bird Counts in Texas 
averaged 28.6 in the 1950's, 7.8 in the 1960's (Oberholser 
1974), and 6.5 from 1970 to 1975 (Christmas Bird Count, 
American Birds — April issues). 

Louisiana. — Always has been very rare (Lowery 
1974). 

Florida. — Available evidence indicates a long-term de- 
cline. Heinzman (1970) estimated 100 birds remaining. 
J. N. Layne (personal communication), in a more exten- 
sive survey, estimated 350-400 remaining. 

Thacker (1971) estimated 55 caracaras held in zoos. 
Breeding has been attempted in zoos (recorded in Inter- 
national Zoo Yearbook 15:333) but breeding potential is 
unknown. 

Reasons for Current Status: Habitat loss is thought to be 
the major factor in caracara declines in the western 
United States (Porter and White 1977) and in Florida 
(Layne 1976). 

In some areas of South America shooting takes a con- 
siderable number: the extinction of the Guadalupe cara- 
cara was caused primarily by shooting. This does not 
appear to be a major factor in U.S. declines, although 
Layne (1976) reported some persecution in Florida. 

Vulture trapping in Florida may have contributed to 
the decline of caracaras. Highway mortality may also be 
a factor. Predator control operations (poison baits) in the 
West may also contribute to mortality (Layne, personal 
communication). 

Management Activities: The Florida Environmental En- 
dangered Lands Program recently acquired an extensive 
parcel of land in Osceola County, Florida, citing preser- 
vation of caracara habitat as one of the reasons for its ac- 
quisition. 

A. R. Phillips, Apartodo Postal 370, San Nicholas de los 
Garza, Nuevo Leon, Mexico, is studying caracara 
populations in Mexico. J. N. Layne, Archbold Biological 
Station, Route 2, Box 180, Lake Placid, Florida 33852, is 
studying the population in Florida. 

Caracara are protected under the United States-Mex- 
ico Migratory Bird Treaty of 10 March 1972. 

Caracaras are monitored by Christmas Bird Counts, 
Texas wildlife refuges (Welder Wildlife Refuge, Laguna 
Atascosa National Wildlife Refuge), Archbold Biological 
Station, Lake Placid, Florida, and roadside wading bird 
and raptor counts in south-central Florida. 

References and Selected Bibliography 

American Ornithologists" Union. 1957. Check-list of North 
American birds. American Ornithologists' Union. Baltimore, 
Md. 691 pp. 

American Ornithologists' Union. 1973. Thirty-second supple- 
ment to the American Ornithologists' Union check-list of North 
American birds. Auk 90(2) :41 1-4 19. 

Arbib. R. 1976. The Blue List for 1977. Am. Birds 30(6):1031- 
1039. 



20 



Baily, H. H. 1925. The birds of Florida. Williams and Wilkins 
Co., Baltimore, Md. 147 pp. 

Batten L. 1969. Common earaeara. Birds of the World 2(9): 
575-577. 

Bent, A. C. 19.37. Life histories of North American birds of 
prey. Part 2. U.S. Natl. Mus. Bull. 170. 482 pp. 

Brown, L., and D. Amadon. 1968. Eagles, hawks, and falcons of 
the world. McGraw-Hill, New York. 2 vols. 945 pp. 

Chancellor, R. D., editor. 1977. World Conference on Birds of 
Prey, International Council for Bird Preservation (ICBP). 
Taylor and Francis, Ltd., London. 442 pp. 

Dillon, O. W. 1961. Notes on nesting of the earaeara. Wilson 
Bull. 73(4) :387. 

Friedmann, H. 1950. Birds of North and Middle America, part 
XL U.S. Natl. Mus. Bull. 50. 793 pp. 

Funderberg, J. B., and G. Heinzman. 1967. Status of the eara- 
eara in Florida. Fla. Nat. 40(4):150-151. 

Glazener. W. C. 1964. Note on the feeding habits of the earaeara 
in south Texas. Condor 66(2): 162. 

Griscom, L., and M. S. Crosby. 1925. Birds of the Brownsville 
region, southern Texas. Auk 42(4): 519-537. 

Grossman, M. L., and J. Hamlet. 1964. Birds of prey of the 
world. C. N. Potter, Inc., New York. 496 pp. 

Haversehmidt, F. 1947. The black vulture and the earaeara as 
vegetarians. Condor 49(5):210. 

Heinzman, G. 1970. The earaeara survev: a four vear report. 
Fla. Nat. 43(4):149. 

Howard, H. 1938. The Rancho La Brea Caracara; a new species. 
Carnegie Inst. Wash. Publ. 487:217-240. 

Howell, A. H. 1932. Florida bird life. Florida Department of 
Game and Fresh Water Fish, Tallahassee. 579 pp. 

Layne, J. N. 1976. Caracara (Caracara cheriway auduboni Cas- 
sin). Pages 757-763 in Florida, Committee on Rare and En- 
dangered Plants and Animals. Rare and endangered biota of 
Florida (Interim microfiche edition). Florida Audubon Society 
and Florida Defenders of Environment. 

Levy, S. H. 1961. The caracara nestingin Arizona. Auk 78(1):99. 

Ligon, J. S. 1961. New Mexico birds and where to find them. 
University of New Mexico Press, Albuquerque. 360 pp. 

Lowery, G. H. 1974. Louisiana birds. Louisiana Wildlife and 
Fisheries Commission. Louisiana State University Press, Baton 
Rouge. 651 pp. 

Monroe, B. L., Jr. 1968. A distributional survey of the birds of 
Honduras. Ornithol. Monogr. 7. 458 pp. 

Oberholser, H. C. 1974. The bird life of Texas (Vol. 1). Uni- 
versity of Texas Press, Austin. 530 pp. 

Phillips,' A., J. Marshall, and G. Monson. 1964. The birds of 
Arizona. University of Arizona Press, Tucson. 220 pp. 

Porter, R. D., and C. M. White. 1977. Status of some rare and 
lesser known hawks in western United States. Pages 39-47 in 
Proceedings of the ICBP World Conference on Birds of Prev — 
Vienna 1975. 442 pp. 

Reichholf. J. 1974. Artenreichtum, Haufigkeit unt Diversitat der 
Greifvogel in einigen Gebieten von Siidamerika. [Species 
richness, abundance and diversity of birds of prev in some re- 
gions of South America.] J. Ornithol. 115(4):381-397. (In Ger- 
man, English summary) 

Richmond. A. R. 1976. Feeding of nestlings bv the caracara in 
Costa Rica. Wilson Rull. 88(4):667. 

Sherrod, S. K. 1978. Diets of North American Falconiformes. 
Raptor Res. 12(3/4):49-121 . 

Smith, A. P. 1910. Miscellaneous bird notes from the lower Rio 
Grande. Condor 12(3): 93- 103. 

Sprunt, A, Jr. 1946. An avian three-in-one: Audubon's caracara. 
Audubon Mag. 48(l):42-44. 

Sprunt, A., Jr. 1954. Florida bird life. Coward-McCann, Inc., 
New York. 527 pp. 

Thacker, R. 1971. Estimations relative to birds of prey in captiv- 
ity in the United States of America. Raptor Res. 5(4): 108-122. 



U.S. Fish and Wildlife Service. 1973. Threatened wildlife of the 
United States. U.S. Fish Wildl. Serv., Resour. Publ. 114. 
289 pp. 

Cooper's Hawk 

(Accipiter cooperi Bonaparte) 

Status: Has suffered severe declines in all areas except the 
western United States. Primary threats include use of 
organochlorine biocides in Central and South America, 
which results in contamination of prey species, and habi- 
tat loss. 

Original Discovery and Description: Falco Cooperii 
Bonaparte, Am. Ornithol., vol. 2, 1828, p. 1, plate 10, 
fig. 1 (near Bordentown, New Jersey). American Orni- 
thologists' Union 1957. 

Background: No close relatives occur in North America; 
the Cooper's hawk is easily confused with the sharp- 
shinned hawk which, although smaller, is very similar in 
appearance. Immature plumages of Cooper's hawk and 
the goshawk are also very similar (Wattel 1973; Brown 
and Amadon 1968). 

Medium-sized woodland hawk preying chiefly on 
medium-sized birds and small diurnal mammals. Con- 
siderable declines occurring in recent years are attributed 
to organochlorine pesticides (Snyder et al. 1973). 

Status Determination: Has been on the Blue List, an 
"early warning" list of species exhibiting potentially ser- 
ious declines, since 1971 (see December issues of Amer- 
ican Birds, 1971 to present). 

Description: A medium-sized accipiter, characterized by 
long legs, long tail, and short rounded wings. Adults dark 
bluish gray above, underparts white, broadly barred 
with rufous or cinnamon, usually more rufous on the 
flanks. Tail relatively long and crossed with three or four 
dark bands. Legs and feet yellow, claws and beak black. 
Females slightly browner above. Iris yellow-orange to 
deep red. Juveniles brownish above, underparts cream 
with dark brown streaks on the breast and variously pat- 
terned on thighs and abdomen. Iris pale yellow; tail, legs, 
and feet same as adult. Adult plumage attained when 1 
year old (Henny and Wight 1972). 

Cooper's hawks exhibit considerable sexual dimorph- 
ism; females average 1.5-1.6 times heavier than males. 
Iris color becomes progressively redder with age: pale yel- 
low in the first year, yellowish orange to reddish orange 
in the second, and deep red by the third or fourth year. 
Eyes of males appear to change faster and also attain 
darker red color than females. Variation in intensity and 
rate of color change precludes establishing precise rela- 
tions between age and eye color (Snvder and Snvder 
1974a; Roberts 1967). 

Breeding Cooper's hawks characteristically use "pluck- 
ing posts" ("butcher block"), where they deplume and 



21 



partially dismember prey before taking it to the nest. 
These areas, with feathers and other body parts strewn 
about, are a good indication of nearby nesting activity 
(Brown and Amadon 1968). 

See Friedmann (1950), Brown and Amadon (1968), 
Wattel (1973), and birding guides for characteristics for 
identification of parts and products. 

Distribution: Breeds in southern Canada and the United 
States south to Mexico. Winters in central and southern 
United States south to Costa Rica (AOU 1957). 

Habitat: Inhabits various types of mixed and deciduous 
forest and open woodland including small woodlots, ri- 
parian woodlands in dry country, open arid pinon wood- 
land, and forested mountainous regions. 

Not as restricted to conifer habitat as the sharp-shinned 
hawk; often nests in deciduous forest. Nests are usually 
near natural or man-made clearings (Meng 1951; Hen- 
nessey 1978) and in proximity to water (Hennessey 1978; 
Reynolds 1978). In Oregon, Cooper's hawks nested in 
50- to 80-vear-old. dense, even-aged conifer stands (Rey- 
nolds 1978). 

During migration and in winter Cooper's hawk occurs 
in almost any type of habitat containing trees or shrubs. 

Feeding Habits: Feeds primarily on medium-sized birds 
such as thrushes, jays, starlings, and quail. Smaller birds 
and larger birds up to the size of adult ruffed grouse are 
also taken. Takes more non-avian prey than the sharp- 
shinned hawk, including mammals up to the size of rab- 
bits and occasionally reptiles and amphibians. In the 
eastern United States, the diet consists of 82% birds and 
18% mammals (Meng 1959; Storer 1966; Wattel 1973), 
whereas in the Southwest up to half the diet is small 
mammals and lizards (Snyder et al. 1973). Mean weight 
of prey was calculated as 37.6 and 50.7 g for males and 
females, respectively (Storer 1966). 

Typically accipitrine. Cooper's hawk still hunts from 
inconspicuous perches and takes its prey by surprise; 
characteristic searching flights utilize available cover for 
concealment. Occasionally it pursues animals on the 
ground, running with considerable speed. 

Reproduction and Development: Nesting begins in early 
to late spring depending on latitude and, to some extent, 
weather. The nest site is selected by the male which does 
most of the building. The nest is constructed of sticks and 
twigs and is lined with flakes of bark (Meng 1951). 

Little is known about mate selection; however, court- 
ship behavior (the male flying around the female with 
outspread under tail coverts) has been observed (Mock- 
ford 1951). Copulation occurs several times a day during 
nest-building and egg-laying. From three to five eggs are 
usually laid; there is some evidence that clutch size is a 
function of habitat quality (Snyder and Snyder 1973). 
Average clutch size in the eastern United States is 4.18, 



with no apparent change from pre-pesticide times (Henny 
and Wight 1972). Eggs are incubated for 35-36 days 
(Meng 1951; Brown and Amadon 1968), primarily by the 
female. The male provides all the food and incubates for 
short periods while the female is eating until the young 
are 2-3 weeks old. 

The young are covered with white down when hatched 
and begin feathering out at 2-3 weeks of age. The male 
provides most of the food for the first 2 weeks, bringing 
the prey almost completely plucked (Meng 1951). The 
female feeds and broods the young. For a typical nest 
containing four young, the adults brought an average of 
6.3 prey animals per day to the nest for 6 weeks (Meng 
1951). Fledging occurs at about 27-30 days for males and 
30-34 days for females; young are dependent on the 
parents for as long as 7 weeks (R. T. Reynolds, personal 
communication), often returning to the nest for feeding 
(Meng 1951). 

Cooper's hawks usually attain sexual maturity at 2 
years of age. However, nesting of 1-year-old birds has 
been recorded (Meng 1951; Hemphill 1966); Henny and 
Wight (1972) estimate that 19% of 1-year-old Cooper's 
hawks attempt to breed. The life-span of Cooper's hawks 
is unknown. Although Meng (1951) estimates that 20 
years may be attained, the maximum recorded life-span 
in the wild is 8 years (Henny and Wight 1972). 

Henny and Wight (1972) estimated immature 
mortality to be 82.5 % and the average annual adult mor- 
tality to be 44.0% for the period 1925-40. From 1941 to 
1947 they estimated immature and annual adult 
mortality to be 77.8 and 34.0%, respectively. 

Diseases and Parasites: The most frequently encountered 
parasites are the nest screwworm fly (Calliphoridae), 
louse fly (Hippoboscidae), and the chewing bird louse 
(Mallophaga); mortality from any of these is very rare. 
Diseases include trichomoniasis, coccidiosis, and aspergil- 
losis. None appear to be limiting factors (Meng 1951). 

Predators and Other Mortality Factors: Predation is lim- 
ited largely to the nesting season; adults may be taken by 
other raptors or large mammals under unusual circum- 
stances. Raccoon predation may be frequent in some 
areas, causing up to 50% nesting failure (Meng 1951). 
Crows, jays, and other typical nest predators will eat eggs 
if the adults are forced away from the nest. Great horned 
owls may prey on nestlings and recendy fledged young; 
however, Cooper's hawks will renest if eggs are destroyed 
early in incubation. 

Severe weather may affect Cooper's hawks. Schriver 
(1969) attributed declines in western Pennsylvania to 
severe winter weather in early 1960. Persistent organo- 
chlorine pesticides cause eggshell thinning as well as out- 
right death of young (Snyder et al. 1973). Populations 
reaching 15-17% shell thinning have serious reproduc- 
tive difficulties (Hickey and Anderson 1968). The effects 
of persistent pesticides are magnified in the longer food 



22 



chains. Therefore, raptors feeding on birds or fish are 
more affected than those feeding on small mammals, 
which, in general, have relatively short food chains (cf. 
Snyder et al. 1973). PCB's and heavy metals (mercury, 
lead) may also contribute to embryonic and early nestiing 
mortality. Shooting pressure appears to have declined 
slowly since 1940 (Henny and Wight 1972). 

Population Level: Cooper's hawk suffered severe declines 
in all parts of its range except the western regions. In the 
northeastern United States, Peterson (1969) estimated 
that the population was less than 10% of its former 
migration count numbers. Hackman and Henny (1971), 
observing fall migration trends, reported annual declines 
of 13% between 1951 and 1961 at White Marsh, Mary- 
land. Robbins (1974) reported similar declines from all 
fall migration indices and all but western Christmas Bird 
Counts. Henny and Wight (1972), using reproductive 
data and mortality rates derived from banding records, 
estimated an annual rate of decline of 13.5% between 
1941 and 1945. Before that, substantially greater shooting 
pressure resulted in even greater rates of decline. After 
1948, concomitant with widespread use of DDT and a 
24.4% drop in the reproductive rate, annual declines 
reached 25% (Henny and Wight 1972). Even this may be 
a gross underestimate as nest failures were apparendy not 
considered (cf. Postupalsky 1974:138). Since 1968, repro- 
duction in the northeastern United States has approached 
that of pre-DDT levels (Braun et al. 1977). In the South- 
west, Cooper's hawk population appeared to be stable up 
to 1971 (Snyder et al. 1973). There the diet is only 50% 
birds, resulting in less pesticide contamination. DDE resi- 
dues in eggs collected in Arizona, New Mexico, and 
Oregon are considerably less than in eggs from Pennsyl- 
vania and New York (Snyder et al. 1973). Reproduction 
appeared normal in the coast range of California and 
Mexico from 1971-1975 (Walton 1975). 

Thacker (1971) estimated seven Cooper's hawks held in 
zoos. An additional number, probably less than 100, are 
held for falconry purposes. Robert Ulbricht (personal 
communication), Hudson, Wisconsin, has successfully 
bred Cooper's hawks. 

Reasons for Current Status: Intensive forest management, 
particularly in western coniferous forests, results in large 
blocks of monotypic habitat, thus reducing potential and 
active nest sites as well as substantial reduction of prey 
species (R. T. Reynolds, personal communication). 

Where the species is much reduced, falconers may have 
a negative effect; some States (e.g., Wisconsin) have 
banned the taking of Cooper's hawks for falconry pur- 
poses. 

Nest predation by raccoons may contribute to reduced 
productivity. In New York, almost half the nests observed 
failed because of raccoon predation (Meng 1951). Rac- 
coon guards placed on nest trees (Meng 1951) and precau- 
tions taken during nesting studies (Fyfe and Olendorff 



1976) greatly decreased raccoon predation. 

Illegal shooting was primarily responsible for early de- 
clines. Cooper's hawk was particularly persecuted be- 
cause of its depredations on poultry. Henny and Wight 
(1972) estimated that shooting mortality of first-year 
birds was 28-47% for 1929-40, 15-24% for 1941^5, 
and 12-21% for 1946-57. With recent improvements in 
legislation, law enforcement, increasing public 
awareness, and changes in human activities and poultry 
management, current illegal shooting mortality is proba- 
bly somewhat less than the estimates for 1946-57. 

Organochlorine pesticides, notably DDE, are 
primarily responsible for the accelerated declines ob- 
served since 1947. Henny and Wight (1972) estimated 
that the annual rate of decline increased from 13.5 to 
25% after the introduction and widespread use of DDT. 
Egg breakage in Arizona and New Mexico, where the 
population appears stable, occurred in at least 11 and 
possibly 15 of 60 clutches; DDE concentrations ranged 
from 1.86 /*g/mL (12.1 ppm dry weight) in fertile eggs to 
6.05 /ig/mL (59.0 ppm dry weight) for broken eggs and 
were correlated with eggshell thinning of 3.0 and 15.7% , 
respectively (Snyder et al. 1973). Eggs from Pennsylvania 
and New York carried considerably higher DDE levels 
ranging from 6.12 to 9.17 (tg/mL. It appears that DDE 
levels above 3^4 /ig/mL results in frequent egg breakage 
and serious declines in productivity (Snyder et al. 1973). 

Management Activities: Protection includes elimination 
of hawk shooting at migration concentration points, and 
public awareness campaigns by Audubon Society, private 
individuals, and law enforcement officials. Cooper's 
hawks are protected under the United States-Mexico 
Migratory Bird Treaty of 10 March 1972. 

Cooper's hawks are monitored by autumn hawk 
counts; the Hawk Migration Association of North Amer- 
ica (HMANA) is establishing standard procedures of ob- 
servation and reporting at the various hawkwatches in 
the United States (J- HMANA 1(1): 1-2). 

Cooper's hawks have been successfully bred in captiv- 
ity. 

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Beebe, F. L. 1974. Field studies of the Falconiformes of British 
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Berger, D. D. 1957. A peculiar type of flight in Cooper's hawks. 
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Borell, A. E. 1937. Cooper hawk eats a flammulatedscreechowl. 
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Boyd, E. M. 1951. The external parasites of birds: a review. Wil- 



23 



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Braun, C. E., J. H. Enderson, C. J. Henny, H. Meng, and 

A. G. Nye, Jr. 1977. Conservation committee report on fal- 
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America. Wilson Bull. 89 (2): 360-369. 
Bromelev, S. W. 1944. The vanishing hawks. Sci. Mon. 58(5): 

373-376. 
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the world. McGraw Hill, New York. 2 vols. 945 pp. 
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Cooper's and sharp-shinned hawks. Am. Birds 27(l):6-7. 
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Duncan, S. 1966. An analysis of the stomach contents of some 

Cooper's hawks (Accipiter cooperii). Auk 83(2):308. 
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Cooper's hawk. Condor 81(2):219-220. 
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their relation to agriculture. U.S. Dep. Agric. Bull. 3. 210 pp. 
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144-154. 
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notes on kidney structure. Anat. Rec. 45(4):381-383. 
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XI. U.S. Natl. Mus. Bull. 50. 793 pp. 
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55(5):761-770. ' 
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White Marsh, Maryland. Chesapeake Sci. 12(3): 137-141. 
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young raptors on the Edwin S. George Reserve. Wilson Bull. 

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Kingbird 16(4):206-209. 
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northern Utah — with special emphasis on the effects of human 

disturbance. M.S. Thesis. Utah State University, Logan. 66 pp. 
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avian species with special reference to changes during the 

modern pesticide era. U.S. Fish Wildl. Serv.. Wildl. Res. Rep. 

1. 99 pp. 
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Pacific Northwest. Trans. N. Am. Wildl. Nat. Resour. Conf. 

42:397-411. 
Henny, C. J., and H. M. Wight. 1972. Population ecology and 

environmental pollution: red-tailed and Cooper's hawks. 

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Fish Wildl. Serv.. Wildl. Res. Rep.' 2. 278 pp. 



Hickey, J. J., and D. W. Anderson. 1968. Chlorinated hydro- 
carbons and eggshell changes in raptorial and fish eating birds. 
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Houston, C. S. 1958. Saskatchewan nesting records of the Cooper's 
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Hubbard, J. P. 1974. The status of the grav hawk in New Mex- 
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Johnson, C. E. 1925. Kingfisher and Cooper's hawk. Auk 42(4): 
585-586. 

Jones, S. 1979. Habitat management series for unique or endan- 
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Kirby, R. E., and M. R. Fuller. 1978. Observations and reinter- 
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598-599. 

Kocan, A. A., J. Snelling, and E. C. Greiner. 1977. Some infec- 
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Koeman, J. H., C. F. van Beusekom, and J. J. M. de Goeij. 
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mammals in the Netherlands. TNO Nieuws 27(10). 

Leopold, A. S. 1944. Cooper's hawk observed catching a bat. 
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goldfinches. Auk 60(4):597. 

Lloyd, G. D., and C. B. Philip. 1966. the "wingless" fly, Camus 
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Mailliard, J. 1908. Cooper hawks attacking crows. Condor 10(3): 
129. 

McDowell, R. D. 1941. The Cooper's hawk in Pennsvlvania. 
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Mead, R. A. 1963. Cooper hawk attacks a pigeon bv stooping. 
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Meng, H. K. 1951. The Cooper's hawk. Ph.D. Thesis. Cornell 
University, Ithaca, New York. 216 pp. 

Meng, H. K. 1959. Food habits of nesting Cooper's hawks and 
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Meyerriecks, A. J. 1957. "Bunching" reaction of cedar wax- 
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Newton, I. 1974. Changes attributed to pesticides in the nesting 
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Newton. I. 1976. Breeding of sparrowhawks (Accipiter nisus) in 
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Newton, I. 1978. Feeding and development of sparrowhawk 
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Newton, I., and M. Marquiss. 1976. Occupancy and success of 
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24 



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Ferruginous Hawk (Buteo regalis Gray) 

Status: Stable or declining slowly; habitat loss poses a 
serious threat. Wide fluctuations in productivity asso- 
ciated with cyclic prey species. 

Original Discovery and Description: Archibuteo regalis 
G. R. Gray, Gen. Birds. Vol. 1, pt. 1, May 1844, plate vi 
(no locality given = Real del Monte, Hidalgo, Mexico). 
American Ornithologists' Union 1957. 

Background: No close relatives occur in North America. 
The ferruginous hawk is the largest of the North Amer- 
ican buteos. R occupies a relatively restricted range in the 
arid western plains region. 

Status Determination: Status Undetermined (U.S. Fish 
and Wildlife Service 1973). Endangered in Oregon 
(Oregon State University Agricultural Experiment Sta- 
tion 1969). On the Blue List, an "early warning" list of 
species exhibiting potentially serious declines, since 1971 
(see December issue of American Birds 1971 to present). 

Description: The largest of the North American buteos, 
with broad rounded wings; commonly observed soaring. 
Adults are brownish above with cinnamon rufous feather 
edgings. Whitish below except for the thighs which are 
rusty-brown with heavy black barring. The tail is whitish 
to silvery, sometimes with cinnamon or reddish colora- 
tion near the end. Eyes are brown and legs and feet are 
yellow. 

Juveniles are similar to the adults, with some spotting 
on the breast and flanks. Thighs are whitish with black 
spotting. Tail is whitish at the base and brownish-gray 
with several indistinct dark bars on the remaining por- 
tion. Eyes, legs, and feet are yellow. The dark, or mela- 



25 



nistic, color phase is characterized by dark brown plum- 
age underneath as well as above. The tail and wings are 
the same as in the light phase, which is usually more com- 
mon (Brown and Amadon 1968). 

Ferruginous hawks are sexually dimorphic; females 
average 1.3 times heavier than males. Howard (1975) 
presented data, utilizing weight and measurements of the 
flexed hallux of nestlings older than 30 days, which 
appear to permit accurate sexing of nestlings. Ferrugi- 
nous hawks, especially in the melanistic phase, may be 
confused with Swainson's, red-tailed, and rough-legged 
hawks under less than optimum field conditions. Brown 
and Amadon (1968) elaborated on field identification of 
these species. 

See Friedmann (1950), Brown and Amadon (1968), 
and birding guides for characteristics for identification of 
parts or products. 

Distribution: Breeds in the semi-arid western plains, 
from southern Alberta, Saskatchewan, Manitoba, and 
eastern North Dakota south to southern Arizona, New 
Mexico, and Kansas (Weston 1969; AOU 1957). Winters 
over much of its breeding range south to Baja California, 
northern Mexico, and Texas, rarely occurring east of the 
Mississippi Biver. 

Habitat: Found primarily in semi-arid western plains re- 
gion (Brown and Amadon 1968; Olendorff 1973). During 
post-breeding and migration these birds occur in high 
mountain shortgrass valleys (L. R. Powers, personal com- 
munication). 

Preferred habitat appears to differ somewhat from re- 
gion to region but generally is characterized by relatively 
unbroken terrain with scattered trees, rock outcrops, or 
tall trees along creek bottoms available for nesting sites 
(Bent 1937; Weston 1969; Howard and Powers 1973; 
Oldendorff 1973). In general, ferruginous hawks remain 
in the southern plains region during the winter (Weston 
1969). 

Feeding Habits: Ferruginous hawks have a relatively re- 
stricted diet when compared with other western buteos, 
consisting primarily of lagomorphs and rodents. In sev- 
eral different studies lagomorphs, primarily black-tailed 
and white-tailed jackrabbits, accounted for up to 
80-95% of prey biomass consumed (Smith and Murphy 
1973; Howard 1975); this apparently coincided with rela- 
tively high points of the jackrabbit cycle. In central North 
Dakota, jackrabbits are infrequently taken; Richardson's 
ground squirrels, northern pocket gophers, and thirteen- 
lined ground squirrels form the bulk of the diet (D. S. 
Gilmer, personal communication). Other sources, includ- 
ing lizards and snakes, are utilized during jackrabbit 
"lows" or on habitat types lacking jackrabbits (Howard 
and Powers 1973; L. R. Powers, personal communica- 
tion). Much of the avian prey consisted of recently 
fledged birds in northeastern Colorado (Olendorff 1973). 



Several methods of hunting are utilized: from a perch, 
while soaring, or more frequently, systematic searching 
and hovering at 12-18 m, and low, rapid flight over open 
country. Nesting birds will hunt cooperatively, especially 
for larger prey like jackrabbits (Howard and Powers 
1973; Snow 1974). Hunting occurs most frequendy near 
sunrise and sunset (Weston 1969). 

Reproduction and Development: Ferruginous hawks uti- 
lize a wide variety of nesting situations including ground 
nests on low hillsides, cutbanks, buttes or small cliffs, in 
short trees in open country, powerline structures, hay- 
stacks, and in tall trees along creek bottoms (Olendorff 
1973). In some areas, many of the tree nests are in man- 
created sites such as shelterbelts and trees around wells or 
dammed creek beds. Nesting activities normally begin in 
March and April and perhaps later in the northern parts 
of its range. 

Little is known about courtship behavior. Three or 
four eggs are typically laid; as many as six have been re- 
corded. Eggs are usually laid in April and are incubated 
primarily by the female (about 35 days); the male takes 
over while she eats. The male provides all the food until 
the young are about 2 weeks old, when the female can 
leave them for increasing periods of time (Weston 1969; 
Howard and Powers 1973). 

Fledging occurs at 38-50 days; males leave first and fe- 
males as long as 10 days later. Males weigh about 1,250 g 
and females 1,800 g at fledging (Schmutz 1977). They are 
dependent on their parents for several weeks after 
fledging (Smith and Murphy 1973). 

Little is known about age of sexual maturity; 2 years 
would be consistent with other species. Two of the oldest 
known records of age are 20 years and 17 years, 3 months 
(Snow 1974). 

Diseases and Parasites: Mortality caused by disease and 
parasites appears to be unimportant. Howard (1975) 
noted myiasis in a low percent of nestlings, but observed 
no mortality. 

Predators and Other Mortality Factors: Great horned 
owls prey on nestlings and recently fledged young 
(Howard 1975). Several instances of coyotes being suc- 
cessfully driven away from the nest have been observed 
(Angell 1969). 

Illegal shooting constitutes a substantial source of mor- 
tality (Salt 1939; Smith and Murphy 1973; Snow 1974; 
Howard 1975). Roadway accidents also frequently cause 
mortality; birds feeding on road kills are in turn hit by 
vehicles. Other causes of mortality include heat prostra- 
tion of nestlings, starvation, and a variety of accidents. 
High winds may cause considerable nest losses (D. S. 
Gilmer, personal communication). 

Population Level: Overall population estimates for the 
ferruginous hawk are lacking. Studies in Idaho and Utah 



26 



(Piatt 1971; Howard and Powers 1973; Smith and 
Murphy 1973; Howard 1975; Powers et al. 1975) indicate 
that present populations are probably holding their own. 
The Blue List for 1976 (Arbib 1975) considers the ferrugi- 
nous hawk as "threatened" in southern Idaho, holding its 
own in east-central Wyoming, declining in Utah, and dis- 
puted as to status in the Southwest. The reasons for these 
differing reports for Idaho and Utah are unclear; on one 
hand there are intense field studies on relatively restricted 
areas, on the other, casual observations over widespread 
areas. One very plausible explanation is the widespread 
crash of jackrabbits in the Utah-Idaho region (82% re- 
duction in numbers) that occurred in late 1972 and 1973 
resulted in a normal depression of nesting (Howard and 
Wolfe 1976). Woffinden (1975) reported very few nesting 
attempts in 1973 in an area supporting over 20 pairs when 
jackrabbit populations were higher (Weston 1969). 
Powers and Craig (1976) reported decreased nesting at- 
tempts in southeastern Idaho in 1975 during the jackrab- 
bit low even though populations of Richardson's ground 
squirrels remained high. The significance of human 
disturbance in these areas is unknown. 

Thacker (1971) estimated 24 ferruginous hawks held 
for research purposes and 2 in zoos. An additional num- 
ber, probably less than 50, are held for falconry purposes. 
Although ferruginous hawks have bred in captivity (Snow 
1974), litde emphasis has been placed on breeding this 
species. 



Reasons for Current Status: Habitat alteration appears to 
be the major cause of declines. Overgrazing often results 
in sagebrush taking over grassland areas. Federal 
agencies are attempting to reclaim these grassland areas 
by various methods, including chaining, plowing, and 
herbicide applications, often reducing nesting and prey 
habitat considerably (Snow 1974; Powers et al. 1975; 
Howard and Wolfe 1976). Of these reclamation tech- 
niques, chaining appears least destructive to the natural 
community (Howard and Wolfe 1976). Proposed geo- 
thermal exploration and increased emphasis on margin- 
ally productive agricultural lands pose a serious threat 
(Howard 1975). Snow (1974) and Howard (1975) made 
recommendations regarding land-use practices that will 
enhance ferruginous hawk habitat. 

Human disturbance during the incubation period ap- 
pears to be a critical factor in nest desertion (Snow 1974; 
Howard 1975; Powers et al. 1975). Field researchers 
quickly recognized the problem and have restricted nest 
visits during this period (Fyfe and Olendorff 1976). The 
number of desertions resulting from spring agricultural 
practices, recreation, and other activities is a matter of 
conjecture but may contribute to declines in some areas. 

See Snow (1974) and Howard (1975) for reclamation 
techniques conducive to maintaining ferruginous hawk 
habitat. Natural fluctuations in jackrabbit cycles may ac- 
count for the current pessimistic attitude maintained in 



some quarters since 1972 (Arbib 1975). Electrocution 
may occur when powerlines are used for perching. 

Management Activities: Modification of powerlines is 
being undertaken by various western power companies to 
reduce deaths by electrocution (Marshall 1940; Miller et 
al. 1975). 

Ferruginous hawks are protected by the United States- 
Mexico Migratory Bird Treaty of 10 March 1972. Migra- 
tion counts are maintained at various hawkwatches 
around the country. 



References and Selected Bibliography 

Adams, R. J., Jr. 1978. A ferruginous hawk in Michigan. Jack- 
Pine Warbler 56(l):51-52. 

Adolphson, D., and G. Jonkel. 1969. Raptor populations com- 
mittee report for 1968. Raptor Res. 3(3):43-57. 

American Ornithologists' Union 1957. Checklist of North Amer- 
ican birds. American Ornithologists' Union, Baltimore, Md. 
691 pp. 

Angell, T. 1969. A study of the ferruginous hawk: adult and 
brood behavior. Living Bird 8:225-241. 

Arbib. R. 1975. The Blue List for 1976. Am. Birds 29(6): 
1067-1072. 

Beebe, F. L. 1974. Field studies of the Falconiformes of British 
Columbia. Occas. Pap. B.C. Prov. Mus. 17. 163 pp. 

Bent, A. C. 1937. Life histories of North American birds of prey. 
Part 1. U.S. Natl. Mus. Bull. 167. 409 pp. 

Biggs, A. 1965. Are the roughlegs (B. regalii) returning? Can. 
Audubon 27 (3): 78-79. 

Bock, C. E., and L. W. Lepthien. 1976. Geographical ecology of 
the common species of Buteo and Parabuteo wintering in 
North America. Condor 78(4):554-557. 

Bowles, J. H.. and F. R. Decker. 1931. The ferruginous rough- 
leg in Washington. Murrelet 12(3):65-70. 

Brown. L.. and D. Amadon. 1968. Eagles, hawks, and falcons of 
the world. McGraw-Hill, New York. 2 vols. 945 pp. 

Brv, E. 1976. The ferruginous hawk. N.D. Outdoors 39(2):1. 

Busch, D. E., W. A. deGraw. and N. C. Clampitt. 1978. Ef- 
fects of handling — disturbance stress on heart rate in the fer- 
ruginous hawk (Buteo regalis). Raptor Res. 12(3/4): 122-125. 

Cameron, E. S. 1914. The ferruginous rough-leg, Archibuteo 
ferruginous, in Montana. Auk 31(2): 159-167. 

Chesser, R. K. 1979. Opportunistic feeding on man-killed prey 
by ferruginous hawks. Wilson Bull. 91(2):330-331. 

Craighead, J. J., and F. C. Craighead. 1956. Hawks, owls, and 
wildlife. Stackpole Co.. Harrisburg, Pa. 443 pp. 

Davy, G. L. 1930. Nesting of the ferruginous roughleg hawk in 
northern North Dakota. Oologist 47(2):14-18. 

Fisher, A. K. 1893. The hawks and owls of the United States in 
their relation to agriculture. U.S. Dep. Agric. Bull. 3. 210 pp. 

Fitzner, R. E., D. Berry, L. L. Boyd, and C. A. Rieck. 1977. 
Nesting of ferruginous hawks (Buteo regalii) in Washington 
1974-1975. Condor 79(2):245-249. 

Friedmann, H. 1950. Birds of North and Middle America, part 
XL U.S. Natl. Mus. Bull. 50. 793 pp. 

Fvfe, R. W. 1976. Status of Canadian raptor populations. Can. 
'Field-Nat. 90(3):370-375. 

Fyfe, R. W., and R. R. Olendorff. 1976. Minimizing the dangers 
of nesting studies to raptors and other sensitive species. Can. 
Wildl. Serv. Occas. Pap. 23. 17 pp. 

Gilmer, D. S., and J. M. Wiehe. 1977. Nesting by ferruginous 
hawks and other raptors on high voltage powerline towers. 
Prairie Nat. 9(1): 1-10. 



27 



Grossman, M. L., and J. Hamlet. 1964. Birds of prey of the 

world. C. N. Potter, Inc., New York. 496 pp. 
Hodson, K. 1968. Porcupine in ferruginous hawk's nest. Blue Jay 

26(4): 180-181. 
Howard, R. P. 1975. Breeding ecology of the ferruginous hawk 

in northern Utah and southern Idaho. M.S. Thesis. Utah State 

University, Logan. 60 pp. 
Howard. R. P., and L. Powers. 1973. Hawk of the desert. Anim. 

Kingdom 76(3):24-27. 
Howard, R. P., and M. L. Wolfe. 1976. Range improvement 

practices and ferruginous hawks. J. Range Manage. 29(1): 

33-37. 
Imler, R. H. 1937. Weights of some birds of prey of western 

Kansas. Bird-Banding 8(4):166-169. 
Jacot, E. C. 1934. An Arizona nest of the ferruginous roughleg. 

Condor 36(2):84-85. 
Jewett, S. G. 1926. The ferruginous roughleg nesting in Oregon. 

Condor 28 (5): 245-246. 
Kocan, A. A., J. Snelling, and E. C. Greiner. 1977. Some infec- 
tious and parasitic diseases in Oklahoma raptors. J. Wildl. 

Dis. 13(3):304-306. 
Lloyd, H. 1937. Twenty-year-old ferruginous roughlegged 

hawk. Can. Field-Nat. 51(9):137. 
Lokemoen, J. T., and H. F. Duebbert. 1976. Ferruginous hawk 

nesting ecology and raptor populations in northern South 

Dakota. Condor 78(4):464-170. 
Marion, W. R., and R. A. Ryder. 1975. Perch site preferences of 

four diurnal raptors in northeastern Colorado. Condor 77(3): 

350-352. 
Marshall, W. H. 1940. An "eagle guard" developed in Idaho. 

Condor 43(2): 166. 
McAfee, W. L. 1935. Food habits of common hawks. U.S. Dep. 

Agric. Circ. 370. 36 pp. 
Miller, D., E. L. Boeker, R. S. Thorsell, and R. R. Olendorff. 

1975. Suggested practices for raptor protection on powerlines. 

Edison Electric Institute, New York. 21 pp. 
Mosher, J. A. 1976. Raptor energetics: a review. Raptor Res. 

10(4):97-107. 
Nelson, M. W., and P. Nelson. 1976. Powerlines and birds of 

prey. Idaho Wildl. Rev. 38(5):3-7. 
Olendorff, R. R. 1972. The large birds of prey of the Pawnee 

National Grassland: nesting habits and productivity 1969- 

1971. Int. Biol. Programme, Grassland BiomeTech. Rep. 151. 

59 pp. 
Olendorff, R. R. 1973. The ecology of the nesting birds of prey 

of northeastern Colorado. Int. Biol. Programme, Grassland 

Biome Tech. Rep. 211. 233 pp. 
Olendorff, R. R. 1974. Some quantitative aspects of growth in 

three species of buteos. Condor 76(4):466^168. 
Olendorff, R. R. 1975. Population status of large raptors in 

northeastern Colorado. Raptor Res. Rep. 3:185-205. 
Olendorff, R. R., and J. W. Stoddart, Jr. 1974. The potential for 

management of raptor populations in western grasslands. Rap- 
tor Res. Rep. 2:47-88. 
Oregon State University Agricultural Experiment Station. 1969. 

Endangered plants and animals of Oregon, III. Corvallis, 

Birds Spec. Rep. 278. 
Piatt, J. B. 1971. A survev of nesting hawks, eagles, falcons, and 

owls in Curlew Valley', Utah. Great Basin Nat. 31(2):51-65. 
Porter, R. D. 1951. The status of rough-legged hawks in Idaho. 

Condor 53(5):257-258. 
Porter, R. D., and C. M. White. 1977. Status of some rare and 

lesser known hawks in western United States. Pages 39-57 in 

Proceedings of 1CBP World Conference on Birds of Prey — 

Vienna, 1975. 442 pp. 
Powers, L. R., and T. H. Craig. 1976. Status of nesting ferrug- 
inous hawks in the Little Lost River Valley and vicinity, south- 



eastern Idaho. Murrelet 57(2):46-47. 
Powers, L. R., R. P. Howard, and C. H. Trost. 1975. Popula- 
tion status of the ferruginous hawk in southeastern Idaho and 
northern Utah. Raptor Res. Rep. 3:153-157. 
Rolfe, E. S. 1896. Nesting of the ferruginous roughleg. Osprey 

1:8-10. 
Salt, W. R. 1939. Notes on recoveries of banded ferruginous 
rough-legged hawks (Buteo regalis). Bird-Banding 10(2):80- 
84. 
Schmutz, J. K. 1977. Relationships between three species of the 
genus Buteo (Aves) coexisting in the prairie-parkland ecotone 
of southeastern Alberta. M.S. Thesis. University of Alberta, 
Calgary. 126 pp. 
Sherrod, S. K. 1978. Diets of North American Falconiformes. 

Raptor Res. 12(3/4):49-121. 
Smith, D. G., and J. R. Murphy. 1973. Breeding ecology of rap- 
tors in the eastern Great Basin of Utah. Brigham Young Univ. 
Sci. Bull. Biol. Ser. 18(3): 1-76. 
Smith, D. G., and J. R. Murphy. 1978. Biology of the ferrugi- 
nous hawk in central Utah. Sociobiology 3(2):79-95. 
Snow, C. R. 1974. Habitat management series for unique or en- 
dangered species. Ferruginous Hawk. U.S. Bureau of Land 
Management Tech. Note 13. 23 pp. 
Snyder, R. L., W. Jenson, and C. D. Cheney. 1976. Environ- 
mental familiarity and activity: aspects of prey selection for a 
ferruginous hawk. Condor 78(1): 138-139. 
Stabler, R. M., and P. A. Holt. 1965. Hematozoa from Colorado 
birds. II. Falconiformes and Strigiformes. J. Parasitol. 51(6): 
927-928. 
Thacker, R. 1971. Estimations relative to birds of prey in captiv- 
ity in the United States of America. Raptor Res. 5(4): 108-122. 
U.s' Fish and Wildlife Service. 1973. Threatened Wildlife of the 
United States. U.S. Fish Wildl. Serv., Resour. Publ. 114. 
289 pp. 
Wakeley, J. S. 1974. Activity periods, hunting methods, and ef- 
ficiency of the ferruginous hawk. Raptor Res. 8(3/4):67-72. 
Wakeley, J. S. 1978a. Activity budgets, energy expenditures, and 
energy intakes of nesting ferruginous hawks. Auk 95(4): 
667-676. 
Wakeley, J. S. 1978fc. Factors affecting the use of hunting sites 

by ferruginous hawks. Condor 80(3):316-326. 
Wakeley, J. S. 1978c. Hunting methods and factors affecting 

their use by ferruginous hawks. Condor 80(3):327-333. 
Ward, B. 1968. Wvoming's ground nesting hawks. Wvo. Wildl. 

32(4): 15-17. 
Weigand, J. P. 1967. Ferruginous hawk attacks great horned 

owl. Auk 84 (3): 433. 
Weston, J. B. 1968. Nesting ecology of the ferruginous hawk 
(Buteo regalis). M.S. Thesis. Brigham Young University, 
Provo, Utah. 40 pp. 
Weston, J. B. 1969. Nesting ecology of the ferruginous hawk 
(Buteo regalis). Brigham Young Univ. Sci. Bull. Biol. Ser. 
10(4):25-36. 
Weston, J. B.,andD. Ellis. 1968. Ground nesting of the ferrugi- 
nous hawk in west-central Utah. Great Basin Nat. 28(3): 111. 
Williams, R. B., and C. P. Mattesor Jr. 1947. Wvoming hawks. 

Wyo. Wildl. 11(4): 15-18. 
Woffinden, N. D. 1975. Ecology of the ferruginous hawk (Buteo 
regalis) in central Utah: population dynamics and nest site 
selection. Ph.D. Thesis. Brigham Young University, Provo, 
Utah. 112 pp. 
Woffinden, N. D., and J. R. Murphy. 1977a. Population dy- 
namics of the ferruginous hawk during a prey decline. Great 
Basin Nat. 37(4):411^25. 
Woffinden, N. D., and J. R. Murphy. 1977b. A roadside raptor 
census in the eastern Great Basin 1973-1974. Raptor Res. 
ll(3):62-66. 



28 



Marsh Hawk 

(Circus cyaneus hudsonius Linnaeus) 

Status: Stable or declining slowly; local habitat loss poses 
the greatest threat to marsh hawks. 

Original Discovery and Description: Falco hudsonius 
Linnaeus, Syst. Nat., ed. 12, vol. 1, 1766, p. 128. Based 
on the Ring-tailed Hawk Pygargus canadensis, Edwards, 
Nat. Hist. Birds, 107 (ad fretum Hudsonis = Hudson 
Bay). American Ornithologists' Union 1957. 

Background: The marsh hawk is the only North Ameri- 
can representative of the harrier family, a family that is 
common in the eastern hemisphere. It usually hunts on 
the wing, systematically quartering fields and marshes, 
covering up to 160 km a day. 

Status Determination: On the Blue List, an "early- 
warning" list of species exhibiting potentially serious de- 
clines, since 1971 (see December issues of American Birds, 
1971 to present). 

Description: A slender-bodied hawk characterized by 
long wings and tail, long slender legs, and a white rump. 

Marsh hawks are sexually dimorphic; females average 
1.4 times heavier than males. Adult males are grayish on 
the head, back, and tail and have a white rump. The tail 
is crossed with six to eight light grayish-brown bands. 
They are white underneath, with cinnamon brown spots 
on the legs and sides. The ends of the outer primaries are 
black. Eyes and legs are yellow. Adult females are 
brownish on the head, back, and tail and have a white 
rump patch. The tail is crossed with six to eight darker 
bands. They are buffy underneath, with brownish to cin- 
namon streaks and spots. The ends of the outer primaries 
are black. Adult plumage is attained at 1 year (Hamer- 
strom 1968). Eyes are brown the first year, becoming 
mostly yellow by the third year (see Hamerstrom 1968). 
Legs are yellow. Juveniles are similar to adult females but 
are darker brown above and are more cinnamon on the 
breast in the fall. Eyes of juvenile males are grayish; eyes 
of females are brown. Legs are yellow. For a more com- 
plete discussion, see Hamerstrom (1968) or Brown and 
Amadon (1968). 

Clark (1972fc) compares various aspects of marsh hawk 
pellets and droppings with those of the short-eared owl, a 
species with similar food habits. Marsh hawk pellets tend 
to have less bone material, 17% by weight, when com- 
pared with short-eared owl pellets, which have 44% 
bone. Droppings of marsh hawks tend to be chalky white 
with a pellet-like greenish to black center. Short-eared 
owls' droppings are buffy with stringy black centers. 

See Friedmann (1950), Brown and Amadon (1968), 
Hamerstrom (1968), or birding guides for characteristics 
for identification of parts or products. 



Distribution: Breeding range extends from northern 
Alaska and Canada south to northern Baja California, 
Mexico, and the southern United States. Absent from the 
southeastern United States. Winters from southern 
Canada to northern South America. Occasionally ob- 
served in the Caribbean chain (AOU 1957). 

Habitat: Inhabits non-forested areas such as marshes, 
grasslands, and prairies for nesting and hunting. Nest sites 
are usually in tall grass in open fields or in marsh areas. 
Winter roosts are in undisturbed fields or marshes. 

Habitat requirements are less specific during the non- 
breeding season; areas far removed from nesting habitat 
are utilized. Communal roost concentrations of up to 
80-90 marsh hawks have been observed in areas of high 
prey density in the winter (Littlefield 1970; Mumford and 
Danner 1974; Weller et al. 1955; Craighead and Craig- 
head 1956). 

Critical Habitat: Marshes, wetlands, and potholes are be- 
ing drained and grasslands are being plowed for agricul- 
ture. 

Feeding Habits: Marsh hawks prey on a wide variety of 
prey including mammals, birds, reptiles, amphibians, 
arthropods, carrion, and even fish (Errington 1933; 
Breckenridge 1935; Randall 1940; Selleck and Glading 
1943; Bond 1947; Long 1961; Proctor 1973). 

Marsh hawks hunt primarily on the wing, systemati- 
cally searching meadows and marshes. Sometimes they 
hunt from low perches. Most hunting is early in the 
morning, with a definite lull during midday; hunting is 
resumed in the late afternoon (Hamerstrom and Wilde 
1973). 

Food habits vary gready with season and geographic 
area. During the breeding season, small to medium-sized 
mammals and birds typically form the bulk of the diet 
with actual proportions dependent upon local abundance 
and availability of prey. Inexperienced juveniles may 
prey more heavily on easily taken amphibians and arthro- 
pods. Small mammal populations may become more im- 
portant for northern wintering marsh hawks with the de- 
parture of migrant birds (Munoff 1963). 

Reproduction and Development: Nesting generally starts 
in middle to late spring. The nest is built by the female; 
the male assists in bringing the nesting material, which is 
largely composed of grasses, weeds, and water plants. 
Nests are usually on the ground; deeper, more bulky nests 
are built in shallow water (Clark 1972a). The general 
nesting area is usually in grasslands or marshy areas 
(Breckenridge 1935; Sealy 1967; Hamerstrom 1969; 
Clark 1972a). Sometimes, nesting is semi-colonial with 
several pairs nesting close together in a large area of con- 
tinuous habitat (Errington 1930a; Hall 1947; Hecht 1951; 
Hamerstrom 1969). High vole populations are associated 



29 



with an increase in the number of nesting marsh hawks 
(Hamerstrom 1979). 

Sky dancing, a ritualized courtship usually performed 
by adult males, appears to be instrumental in male selec- 
tion and advertisement of territory. But males not con- 
nected with a territory also sky dance (Hamerstrom 
1969). Females rarely sky dance. Copulation is rarely ob- 
served and little is known about frequency or location 
(Hamerstrom 1969). Clark (1972a) saw one pair copulat- 
ing on a fence post. From three to six eggs are usually 
laid; the incubation period is 23-26 days. Females incu- 
bate the eggs; males have rarely been observed on the nest 
(Christensen and Trelease 1941; Hamerstrom 1969). The 
male provides essentially all food during incubation and 
the early nestling period, usually dropping food to the fe- 
male in an aerial food transfer. If the female is absent, he 
drops the food at the nest and leaves (Hecht 1951). 

At hatching the young are covered with white down; 
the juvenile plumage appears at about 2 weeks of age. 
Munoff (1963) found that greatest weight increases oc- 
curred during the second week and the greatest rate of 
primary growth during the third and fourth weeks. The 
young wander from the nest before they are able to fly, 
usually forming a well-developed trail system in the sur- 
rounding vegetation. Young males fledge at 31-34 days 
and females at 35-38 days (Scharf and Balfour 1971). 

Hamerstrom (in Schmutz and Schmutz 1975) observed 
16 subadult females and 3 subadult males (1 year old) of 
163 breeding adults. She found successful breeding to at 
least 7 years. Kennard (1975) reported the longest known 
life-span as 16 years, 5 months. Hickey (1952) estimated 
the immature mortality rate to be 59% and the average 
annual adult mortality rate to be 30%. 

Diseases and Parasites: Little is known about diseases and 
parasites. Scharf (1966) reported louse flies (Hippobosci- 
dae) on marsh hawks. Nest screwworm flies (Calliphori- 
dae) are commonly associated with those raptors having 
bulky nests with damp interiors (Sargent 1938). 

Predators and Other Mortality Factors: The ground- 
nesting habits of marsh hawks render them more vulner- 
able than most other raptors to a much wider range of 
predators and other problems, except wind. Hamerstrom 
(1969) included deer, cattle, skunk, and carrion beedes as 
known causes of nestling mortality. Many other mam- 
malian, reptilian, and avian predators may prey upon 
eggs and young. Weller et al. (1955) found remains of five 
dead marsh hawks on a winter roost in central Missouri. 
Although some were apparently killed by mammals, one 
was killed and eaten by a great horned owl. 

Nests are destroyed by haying and other agricultural 
operations. Prolonged rains may drown out nests in 
marshes. As with many raptors, shooting continues to be 
a considerable source of mortality. Hamerstrom (1969, 
1970) attributed deterioration of reproductive behavior 
to pesticide contamination. The number of nests on her 



study area is back to normal since the ban on DDT 
(Hamerstrom 1979). 

Population Level: The population status of the marsh 
hawk is unclear. It appears that declines occurred to a 
greater extent in the eastern United States than in the 
West (Arbib 1973). Hackman and Henny (1971) indi- 
cated a 7% annual decline in observations of fall migrant 
marsh hawks from 1951 to 1961. Hamerstrom (1979) 
found a close association between numbers of nesting 
marsh hawks and vole abundance. During locally heavy 
DDT application (1965-68) nesting marsh hawks failed 
to respond to a vole high. Nesting in pre- and post-DDT 
years was comparable. Numbers of migrants showed a 
70% decline from 1960 to 1969. Brown (1973) showed a 
general decline of winter populations through 1965 and 
an increase from 1966 to 1969. At this time (1980) the 
marsh hawk population does not appear to be in serious 
trouble; however, adequate knowledge of population 
parameters is lacking. 

Thacker (1971) estimated a total of seven marsh hawks 
in captivity, primarily in zoos. Marsh hawks are rarely 
used for falconry. Captive breeding of this species has not 
received much attention. 

Reasons for Current Status: Extensive draining of wet- 
lands and monotypic farming have probably had the 
severest impact on the marsh hawk (Lokemoen and 
Duebbert 1976). 

Illegal shooting may be considerable in some areas but 
appears to be declining. 

Pesticide contamination does not appear to be a signifi- 
cant factor at this time. Local populations may have been 
affected by agricultural pesticides (Hamerstrom 1969, 
1970, 1979). 

Management Activities: None specifically for marsh 
hawks at this time; however, wetland preservation aimed 
primarily at waterfowl and habitat management pro- 
grams for other species (e.g., prairie chickens, see Hamer- 
strom 1969) are also beneficial to marsh hawks. 

Marsh hawks are protected under the United States- 
Mexico Migratory Bird Treaty of 10 March 1972. 

Migration counts have been established at various 
hawk watches around the country (see Newsletter of the 
Hawk Migration Association of North America). 

References and Selected Bibliography 

American Ornithologists' Union. 1957. Check-list of North 

American birds. American Ornithologists' Union. Baltimore, 

Md. 691 pp. 
Arbib, R. 1973. The Blue List of 1974. Am. Birds 27(6):943-945. 
Balfour, E. 1957. Observations on the breeding biology of the 

hen harrier in Orkney. Bird Notes 27:17-183. 
Balfour, E. 1962. The nest and eggs of the hen harrier in Orkney. 

Bird Notes 30:69-73. 
Balfour, E. 1962-1963. The hen harrier in Orkney: courtship. 



30 



display and sociability. Bird Notes 30:145-153. 

Balser. D. S., H. H. Dill, and H. K. Nelson. 1968. Effect of 
predator reduction on waterfowl nesting success. J. Wildl. 
Manage. 32(4):669-682. 

Bandy, L. W., and B. Bandy. 1978. Marsh hawks follow hunt- 
ing red fox. Wilson Bull. 90(1): 133-134. 

Baumgras, P. S. 1942. An unusual clutch of marsh hawk eggs. 
Wilson Bull. 54(1):50. 

Beebe, F. L. 1974. Field studies of the Falconiformes of British 
Columbia. Occas. Pap. B.C. Prov. Mus. 17. 163 pp. 

Bent, A. C. 1937. Life histories of North American birds of prev. 
Part 1. U.S. Natl. Mus. Bull. 167. 409 pp. 

Berger, D. D. 1956. Marsh hawk pursues domestic cat. Auk 
73(2): 288. 

Berger, D. D. 1958. Marsh hawk takes prev from short-eared 
owl. Wilson Bull. 70(1):90. 

Berger, D. D., F. Hamerstrom, and F. N. Hamerstrom, Jr. 1963. 
The effect of raptors on prairie chickens on booming grounds. 
J. Wildl. Manage. 27(4):778-791. 

Beske, A. E. 1978. Harrier radio-tagging techniques and local 
and migratory movements of radio-tagged juvenile harriers. 
M.S. Thesis. University of Wisconsin, Stevens Point. 47 pp. 

Beske, A. E., and J. Champion. 1971. Prolific nesting of short- 
eared owls on Buena Vista marsh. Passenger Pigeon 33(2): 
99-103. 

Bildstein, K. L. 1976. Behavior of wintering northern harriers 
(Circus cyaneus hudsonius) and other raptorial birds at com- 
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31 



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32 



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Merlin (Falco columbarius Linnaeus) 

Status: Severe declines in Richardson's merlins (Falco 
columbarius richardsonii) due to habitat loss and 
reproductive difficulties appear to have leveled out. 
Taiga and black merlin populations appear stable after 
slight declines. Primary threats include habitat loss to 
Richardson's merlin and continued use of organochlorine 
biocides in Central and South America which results in 
contamination of prey species. 

Original Discovery and Description: Eastern or taiga 
merlin (F. c. columbarius Linnaeus): Falco columbarius 
Linnaeus, Syst. Nat., ed. 10, vol. 1, 1758, p. 90. Based on 
The Pigeon Hawk Accipiter palumbarius (Catesby, Caro- 
line, Vol. 1, p. 3, plate 3; in America = South Carolina). 
American Ornithologists' Union 1957; Temple 1972/;. 

Richardson's merlin (F. c. richardsonii Ridgway): 
Falco Hypotriorchis richardsonii Ridgway, Proc. Acad. 
Nat. Sci. Philadelphia, 22, no. 3, Aug. -Dec. 1870 (Mar. 
14, 1871), p. 145 (mouth of the Vermillion River, South 
Dakota). AOU 1957. 

Black merlin (F. c. suckleyi Ridgway): Falco colum- 
barius var. Suckleyi Ridgway, bull. Essex Inst., 5, No. 
12. Dec. 1873 (Feb. 1874), p. 201 (Shoalwater Bay, 
W.T., Ft. Steilacoom = Shoalwater Bay, Washington). 
AOU 1957. 

Western or taiga merlin (F. c. bendirei Swann): Falco 
columbarius bendirei Swann, Bull. Rrit. Orn. Club, 42, 



no. 264, Feb. 2, 1922, p. 66 (Fort Walla Walla, Wash- 
ington State). AOU, 1957; Temple 1972b. 

Background: Temple (1972b) discussed the systematics of 
North American merlins. On the basis of phenotypic and 
phylogenetic characteristics he considers F. c . columbar- 
ius, F. c. richardsonii, and F. c. suckleyi taxonomically 
distinct. There appears to be no basis for separating F. c. 
bendirei and he suggests considering it a synonym of F. c. 
columbarius (cf. AOU 1957). 

The merlin is a small falcon of panboreal distribution. 
Four subspecies are currently recognized as occurring in 
North America (AOU 1957, but see Temple 1972b). Preys 
chiefly on small to medium-sized birds. Declines in recent 
years are primarily pesticide related. 

Status Determination: The merlin has been on the Blue 
List, an "early warning" list of species exhibiting poten- 
tially serious declines, since 1971 (see December issues of 
American Birds, 1971 to present). F. c. columbarius and 
F. c . richardsonii are considered as Status Undetermined 
by the U.S. Fish and Wildlife Service (1973). 

Richardson's merlin is listed as Endangered in Canada 
(Godfrey 1970). 

Description: A small to medium-sized falcon, charac- 
terized by long pointed wings and long-appearing tail. 
Adult males are slaty blue-gray above, varying from light 
gray to nearly black. Underneath buffy with prominent 
cinnamon to black streaking. Tail is dark with three to 
five gray or buff bands. Adult females and juveniles are 
similar to adult male, but are dark brownish above in- 
stead of bluish. Adult plumage is attained when 1 year 
old (Temple 1972c). 

Merlins are sexually dimorphic; females average 1.3 
times heavier than males. Adult and immature females 
are very similar; however, the rump and upper tail co- 
verts of adult females are slate brown in contrast to the 
brown dorsal plumage. Immatures lack this contrast. Im- 
mature males have grayish bands in the tail, whereas im- 
mature females have buffy bands. There are considerable 
differences in coloration of subspecies. F. c . richardsonii 
is characteristically lighter colored and F. c. suckleyi is 
considerably darker. For a more comprehensive discus- 
sion, see Temple (1972b, 1972c). See Friedmann (1950), 
Brown and Amadon (1968), Temple (1972b, 1972c), and 
birding guides for characteristics for identification of 
parts or products. 

Distribution: 

Taiga merlin. — Breeds in the boreal forest regions of 
Canada, Alaska, and northern United States. Winters in 
the western United States and Canada, along the Gulf 
and Eastern coasts, and south to northern South America 
(Temple 1972b; AOU 1957). 

Richardson's merlin . — Breeds in the prairie-parkland 
regions of central Canada and the northern Great Plains. 



33 



Winters from the northern Great Plains south to northern 
Mexico (AOU 1957; Temple 1972b). 

Black merlin. —Breeds in the humid Pacific Coastal re- 
gions and on offshore islands. Primarily resident; some 
birds range throughout the western United States during 
winter (AOU 1957; Temple 1972b). 

The southern limit of breeding range of the taiga 
merlin is now somewhat farther north due to human en- 
croachment. Agricultural land-use patterns have affected 
much of the habitat of Richardson's merlin (Fyfe 1972). 

Habitat: Taiga merlins breed in the boreal forest biome. 
Nests are usually found in coniferous trees near open areas 
such as forest edges, bogs, and lakes. Nesting near water 
appears to be common. Although few nests of the black 
merlin have been described, it appears that their habitat 
requirements are similar to those of the taiga merlin. 
Richardson's merlins breed in the prairie-parkland biome 
in the northern Great Plains. Nests are usually found near 
water, in isolated groves of trees on the prairies, and 
wooded areas along rivers. Nests in deciduous trees are 
common (Fox 1964). 

Merlins, as is common with falcons, do not build their 
own nests but utilize nests built by other species. Old nests 
of crows, ravens, magpies, and various species of hawks 
are usually used. Near the arctic treeline the eggs are 
often laid in a scrape in the soil under bushes or small 
trees. Ground nesting has never been recorded for 
Richardson's merlin, although nesting has been observed 
in tree cavities and in old magpie nests on cliffs. They 
have been breeding successfully in Saskatoon, Manitoba 
(Oliphant 1974), and several other cities (Trimble 1975; 
McCowan 1978). 

Wintering taiga and black merlins utilize a wide 
variety of habitat types, almost any type encountered in 
their winter range. Richardson's merlins tend to remain 
in prairie habitat even in winter (Fox 1964). 

Critical Habitat: Richardson's merlins nest in small 
groves of trees on areas of prairies, especially near water. 

Feeding Habits: Merlins prey almost entirely on small to 
medium-sized birds. Mammals, other than bats, are very 
rarely taken. Dragonflies and other insects may form part 
of the diet during summer and fall, especially for young 
merlins just learning to hunt (Williams and Matteson 
1947; Lawrence 1949; Bond 1951; Street 1960; Eyre and 
Paul 1973). 

Merlins often hunt in a manner similar to accipiters, 
utilizing inconspicuous perches and searching flights to 
surprise potential prey. If the first strike fails, pursuit is 
continued with a series of short stoops (Brown and 
Amadon 1968). Merlins will also take prey by stooping 
from great heights in the manner of the larger falcons 
(Laing 1938; Craighead and Craighead 1940). 

Reproduction and Development: Nesting begins in early 
to late spring depending on latitude and, to some extent. 



weather. Males arrive on the breeding areas as much as a 
month before the females. Nests are seldom reused: how- 
ever, ground nest scrapes have been used for as long as 23 
years (S. A. Temple, personal communication). 

Males usually select the nest site and attract females 
with vocalizations and display. Average clutch size for all 
populations is 4.8 eggs per clutch (Temple 1970:42). Eggs 
are incubated 28-32 days, mostly by the female. How- 
ever, males may contribute substantially; they were on 
the nest about 1/3 of the time birds were flushed from the 
nest in Newfoundland (Temple 1972c). 

The young are covered with white down and begin 
feathering out at 2-3 weeks of age. The male provides 
most of the food for the first two weeks, bringing the prey 
unplucked. The female plucks the prey and feeds it to the 
young. When the young no longer need constant brood- 
ing, the female also hunts. The young fledge at 25-35 
days, remaining dependent upon the parents for up to 5 
weeks after fledging (Lawrence 1949; Fox 1964; Brown 
and Amadon 1968; Eyre and Paul 1973; Oliphant 1974). 

It appears that merlins may breed successfully when 1 
year old; however, most birds probably do not breed until 
they are 2 years old (Temple 1972c). The life-span of mer- 
lins is unknown; a tentative maximum of 8-10 years is 
probably consistent with that of other species. 

Diseases and Parasites: Diseases and parasites do not 
appear to pose a significant threat to merlin populations. 
Parasites most frequently encountered include nest screw- 
worm flies (Calliphoridae), louse flies (Hippoboscidae; 
Mueller et al. 1969), chewing bird lice (Mallophaga), and 
Simulium flies (Trimble 1975). Diseases include tricho- 
moniasis, coccidiosis, and aspergillosis (Beebe and 
Webster 1964). 

Predators and Other Mortality Factors: Predation is 
limited primarily to the nesting season; adults may be 
taken at other times by other raptors or large mammals 
under unusual circumstances. Crows, jays, and other 
typical nest predators will eat eggs if the adults are forced 
away from the nest. However, merlins will renest if the 
eggs are destroyed early in incubation. Great horned owls 
and other owls may prey on nestlings and recently fledged 
young. 

Severe storms may result in the loss of eggs and the 
death of nestlings (Oliphant 1974). Although illegal 
shooting probably had a detrimental impact in earlier 
years, it does not now appear to be a major mortality 
factor (Fyfe 1977). Persistent organochlorine pesticides. 
PCB's, and heavy metals cause eggshell thinning, aber- 
rant reproductive behavior of adults, and embryonic 
mortality (Temple 1972a). The most serious declines have 
occurred in the typically agricultural regions inhabited 
by Richardson's merlin (Fyfe 1972; Trimble 1975). 

Population Level: Richardson's merlin has suffered con- 
siderable declines due to habitat loss and DDE-induced 



34 



eggshell thinning. Taiga and black merlins may have suf- 
fered slight declines, especially during the era of heavy 
DDT use (Fox 1971; Trimble 1975). Oliphant and 
Thompson (1978) reported production in Saskatchewan 
Richardson's merlins from 1970 to 1977 as comparable to 
pre-1950 levels. Restrictions on the use of DDT and other 
persistent pesticides offer encouragement for the future. 
Although meaningful increases have not been noted, de- 
clines do not appear to be continuing (Fyfe 1972). 

Thacker (1971) estimated 22 merlins (not broken down 
to subspecies) held for research purposes and 2 in zoos. An 
additional number, probably less than 50, are held for 
falconry purposes. Several people have been successful in 
breeding merlins, including John Campbell, Rlack 
Diamond, Alberta, and Richard W. Fyfe, Canadian 
Wildlife Service (Trimble 1975). 

Reasons for Current Status: Agricultural practices on the 
Great Plains, such as cutting and burning around prairie 
potholes, have severely reduced Richardson's merlin habi- 
tat, including nesting sites and adequate prey habitat 
(Fyfe 1975). Richardson's merlin appears to be shifting its 
range somewhat to compensate for habitat changes. Fox 
(in Trimble 1975) predicted increased nesting in 
Montana, Wyoming, and the Dakotas, although recent 
variability of weather patterns may result in declines of 
agricultural expansion on the Canadian prairies. Taiga 
and black merlins have not suffered substantial habitat 
losses; however, recent interest in peat fuels as an energy 
source may be construed as a potential threat to habitat of 
taiga merlins. 

Organochlorine pesticides are primarily responsible for 
declines in productivity, especially in the more contami- 
nated prairie regions inhabited by Richardson's merlin. 
However, recent changes in chemical seed treatments 
eliminating dieldrin, heptachlor, and mercury, and re- 
strictions of DDT use give cause for guarded optimism re- 
garding reproductive difficulties (Fyfe 1972). 

Management Activities: Restrictions on DDT use in the 
United States and Canada. Merlins were added to United 
States-Mexico Migratory Rird Treaty on 10 March 1972. 

Richard Fyfe is monitoring reproductive success in Al- 
berta. Migration counts are maintained at various hawk- 
watches around the country (see Newsletter of Hawk 
Migration Association of North America). 

John Campbell, Rlack Diamond, Alberta, reared four 
young in 1974, the first successful captive propagation. 
Richard Fyfe obtained fertile eggs in 1974, but none 
hatched; however, three young fledged in 1975. 

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36 



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37 



48(6):97. 
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Northern Aplomado Falcon (Falco femoralis 
septentrionalis Todd) 



Status: Peripheral — Rare. 

Original Discovery and Description: Falco femoralis sep- 
tentrionalis Todd: Falco fuscocoerulescens septentrionalis 
Todd, Proc.-Biol. Soc. Washington, 29, June 6, 1916, 
p. 98 (Fort Huachuca, Arizona). American Ornitholo- 
gists' Union 1957. The original discovery of the aplomado 
falcon was made in 1853 by Dr. A. L. Heerman in south- 
ern New Mexico (Baird 1858). 

Background: The range of the northern aplomado falcon 
extends south to northern Guatemala where it evidendy 
intergrades with F. }. femoralis, whose range extends 
south to Patogonia (Howell 1972). 

The aplomado falcon is a medium-sized falcon inhab- 
iting the extreme southwestern United States. It is cur- 
rently ranked ninth on the American Birding 
Association's list of most desired bird sightings in the 
United States (West 1979). 

Status Determination: Listed as Status Undetermined by 
the U.S. Fish and Wildlife Service (1973). The aplomado 
falcon is listed in Appendix II of the Convention on Inter- 
national Trade in Endangered Species of Wild Flora and 
Fauna (USFWS 1978). It also receives special protection 
in Texas, Arizona, and New Mexico, where it formerly 
nested (Hector and Knopf 1979). 

Description: Medium-sized falcon; adults are bluish gray 
above, slightly darker on the crown; tail blackish with 
white bars and a white tip. A buffy line extends back 
from each eye, often joining to form a collar on the neck. 
A broad black stripe extends below and behind the eye 
and joins a narrow black malar stripe. Throat and cheeks 
are white or buffy and breast is buffy. Sides and a band 
across the belly are black with white feather edgings. 
Cere and legs yellowish, eye dark brown. Immatures are 
blackish brown above with less distinct tail bars. Eye- 
stripe, breast, and abdomen deep cinnamon to orangish, 
fading to whitish as the season progresses. Breast immac- 
ulate or with black streaking. Eye brown (Brown and 
Amadon 1968). 

Sexes colored alike, females are larger. Males, wing 
248-267 mm, tail 172-193 mm; females, wing 
272-302 mm, tail 192-307 mm (Brown and Amadon 
1968). See Brown and Amadon (1968:187, plate 156), 
Oberholser (1974), and birding guides for characteristics 
for identification of parts and products. 

Distribution: Breeds from northern Guatemala north to 
Arizona, New Mexico, and Texas (AOU 1957). The extent 



of winter movements are unclear; northern birds may 
move into central Mexico (Bent 1938). However, col- 
lected specimens and observations in the United States are 
most abundant from September to December, which sug- 
gests the possibility of year-round residency by this species 
(Dean Hector, personal communication). 

Arizona. — Locally common summer (or permanent?) 
resident in southeast Arizona before 1890; since then vir- 
tually extirpated — three records, one before 1910, one on 
11 November 1939, and one on 7 October 1940 (Ligon 
1961). 

New Mexico. — Locally common in open valley and 
prairie land in southwestern New Mexico west of the 
Guadalupe Mountains. Now very - rare: generally con- 
fined to open yucca desert land west of the Rio Grande al- 
though a pair was observed east of the Rio Grande on 11 
May 1962, in Lea County. One nesting record in 1952 
(Ligon 1961; Porter and White 1977). 

Texas. — Locally common in southwest Texas, common 
in southern Texas between Brownsville and Point Isabel 
(Smith 1910; Strecker 1930; Griscom and Crosby 1925). 
Populations declined severely between 1890 and 1910; 
there has been one breeding record since 1910, a nest with 
three eggs found on 13 March 1941, in southern Brooks 
County (Oberholser 1974; Porter and White 1977). 

Habitat: The aplomado falcon inhabits grassy plains and 
valleys with scattered mesquite, yucca, and cactus (Ober- 
holser 1974). 

Aplomado falcons require nesting platforms such as 
stick nests of con ids and raptors in desert terrain. Other 
sites, such as bromeliads, are used in the tropics (Dean 
Hector, personal communication). 

Critical Habitat: Uncertain; preferred habitat require- 
ments are little known. 

Feeding Habits: Aplomado falcons are primarily bird 
hawks and take species ranging from the size of rock 
doves (Brown and Amadon 1968) and brown jays (about 
250 g) to seedeaters and warblers (about 30-40 g). They 
also feed on insects, primarily cicadas, locusts, and 
beetles (Dean Hector, personal communication). 

Typically hunts from perches, interspersed with 
searching flights. Pairs are often observed hunting 
together after sundown (Ligon 1961). They also have 
been observed catching insects stirred up by advancing 
grass fires (Brown and Amadon 1968: Oberholser 1974). 

Reproduction and Development: Nesting begins in late 
March and April. The aplomado falcon uses old nests of 
other species, often those of the white-necked raven. 
usually in vucca, mesquite, or cacti (Ligon 1961; Brown 
and Amadon 1968; Oberholser 1974). 

Little is known about courtship behavior. From two to 
four eggs, usually three, are laid (Ligon 1961; Oberholser 
1974). Both parents are known to incubate (Brown and 
Amadon 1968). Incubation period is unknown but is 



38 



probably around 28-32 days. 

Predators and Other Mortality Factors: Organochlorine 
contamination and concomitant eggshell thinning has 
been reported in the aplomado falcon. The extent of 
DDE-induced eggshell thinning in Mexican populations 
appears similar to other populations of bird-eating 
raptors experiencing severe reproduction difficulties due 
to DDE contamination. Eggshells collected between 1957 
and 1966 and in 1977 averaged 25.4 and 24 % thinner, re- 
spectively, than pre-DDT eggshells (Kiff et al. 1980). 

Population Level: The last nesting record for the United 
States was in 1952; however, the aplomado falcon was 
locally common in the southwestern United States before 
1900 (Porter and White 1977). 

Breeding potential is probably fair, considering recent 
advances in the breeding of large falcons. Three 
aplomado falcons in the Oklahoma City Zoo exhibited 
courtship behavior but did not reproduce (Snelling and 
Lueck 1976) and have since been separated (Dean Hec- 
tor, personal communication). Several birds have been 
kept for falconry purposes in Arizona and California 
(Dean Hector, personal communication). 

Management Activities: Leaving scattered trees standing 
in the implementation of range management practices de- 
signed to reduce brush-encroached areas would provide 
potential nest sites for aplomado falcons. 

Dean P. Hector, Oklahoma State University, is con- 
ducting a study of the aplomado falcon which will at- 
tempt to answer the following questions: (1) What is the 
present status of this species in the United States? (2) 
What constitutes preferred habitat for the species? (3) Do 
areas presently exist in the United States that could sup- 
port populations of the aplomado falcon? (4) How is con- 
tinuing DDT use in Mexico affecting the productivity of 
the species? (5) What is the general and hunting behavior 
ecology of this species in Mexico? (6) What is the cause of 
decline in the United States? 

Aplomado falcons are protected under the United 
States-Mexico Migratory Bird Treaty of 10 March 1972. 

References and Selected Bibliography 

American Ornithologists' Union. 1957. Check-list of North 
American birds. American Ornithologists' Union, Baltimore, 
Md. 691 pp. 

Bailey, F. M. 1928. Birds of New Mexico. New Mexico Depart- 
ment of Game and Fish. 807 pp. 

Baird. S. R. 1858. Birds: raptores. Explorations and Surveys for a 
Railroad Route from the Mississippi River to the Pacific Ocean 
9:4-64. 

Bendire, C. E. 1892. Life histories of North American birds. 
U.S. Natl. Mus. Spec. Bull. 1. 

Bent, A. C. 1938. Life histories of North American birds of prey. 
Part 2. U.S. Natl. Mus. Bull. 170. 482 pp. 

Brandt. H. 1951. Arizona and its bird life. The Bird Research 
Foundation, Cleveland, Ohio. 



Brooks, A. 1933. Some notes on the birds of Brownsville, Texas. 

Auk 50(l):59-63. 
Brown, L., and D. Amadon. 1968. Eagles, hawks and falcons of 

the world. McGraw-Hill, New York. 2 vols. 945 pp. 
Chancellor, R. D., editor. 1977. World conference on birds of 

prey, International Council for Bird Preservation (ICBP). 

Taylor and Francis, Ltd., London. 442 pp. 
Fisher, A. K. 1893. The hawks and owls of the United States in 

their relation to agriculture. U.S. Dep. Agric. Bull. 3. 210 pp. 
Friedmann, H. 1925. Notes on the birds observed in the lower 

Rio Grande Vallev of Texas during Mav, 1924. Auk 42(4): 

537-554. 
Friedmann, H. 1950. Birds of North and Middle America, part 

XL U.S. Natl. Mus. Bull. 50. 793 pp. 
Griscom, L., and M. S. Crosby. 1925. Birds of the Brownsville 

region, southern Texas. Auk 42(4):519-537. 
Grossman, M. L., and J. Hamlet. 1964. Birds of prey of the 

world. C. N. Potter, Inc., New York. 496 pp. 
Harris, B. K. 1964. Recent bird records from southeastern New 

Mexico. Condor 66(2): 159-161. 
Hector, D. P. 1980. Our rare falcon of the desert grassland. 

Birding 12(3):92-109. 
Hector. D. P. 1981. The habitat, diet, and foraging behavior of 

the aplomado falcon Falco femoralis (Temminck). M.S. 

Thesis. Oklahoma State University, Stillwater. 189 pp. 
Hector, D. P.. and F. L. Knopf. 1979. Official status of the 

aplomado falcon, February 1979. Oklahoma State University, 

Stillwater. 1 p. (Unpubl. rep.) 
Howell, T. R. 1972. Birds of the lowland pine savannah of 

northeastern Nicaragua. Condor 74(3):316-340. 
Johnson. A. W. 1965. The birds of Chile and adjacent regions of 

Argentina, Bolivia, and Peru. Pages 270-272 in Piatt Estab- 

lecimientos, Graficos S. A., Buenos Aires, I. 
Kiff, L. F., D. B. Peakall. and D. P. Hector. 1980. Eggshell 

thinning and organochlorine residues in the bat and aplomado 

falcons in Mexico. Proc. Int. Ornithol. Congr. 17:949-952. 
Lane, ]. A. 1965. A birder's guide to southeastern Arizona. L & P 

Photography, Box 19401, Denver, CO 80219. 
Lawrence, G. N. 1874. The birds of west and northwest Mexico, 

based upon collections made by Col. A. J. Grayson, Capt. ]. 

Xanthus, and Ferd. Bischoff, now in the museum of the 

Smithsonian Inst, at Washington, D. C. Mem. Boston Cos. 

Nat. Hist. 2:265-319. 
Ligon, J. S. 1961. New Mexico birds and where to find them. 

University of New Mexico Press, Albuquerque. 360 pp. 
Merrill, J. C. 1878. Notes on the ornithology of southern Texas, 

being a list of birds observed in the vicinity of Fort Brown, 

Texas from Feb. 1876 to June 1878. Proc' U.S. Natl. Mus. 

1:118-173. 
Monson, G., and A. R. Phillips. 1964. A checklist of the birds of 

Arizona. University of Arizona Press. Tucson. 74 pp. 
Oberholser, H. C. 1974. The bird life of Texas. University of 

Texas Press, Austin. Vol. 1. 530 pp. 
Porter, R. D., and C. M. White. 1977. Status of some rare and 

lesser known hawks in western United States. Pages 39-57 in 

Proceedings of the ICBP World Conference on Birds of Prev 

-Vienna, 1975. 442 pp. 
Sherrod, S. K. 1978. Diets of North American Falconiformes. 

Raptor Res. 12(3/4):49-121. 
Smith, A. P. 1910. Miscellaneous bird notes from the Lower Rio 

Grande. Condor 12(3):93-103. 
Snelling, J. C, and B. E. Lueck. 1976. Predatory behavior of 

aplomado falcons in captivity. Avic. Mag. 82(3): 169-171. 
Strecker, J. K. 1930. Field notes on western Texas birds (part 

one). Contrib. Baylor Univ. Mus. 22:1-14. 
Thacker, R. 1971. Estimations relative to birds of prey in captiv- 
ity in the United States of America. Raptor Res. 5(4): 108-122. 
U. S. Fish and Wildlife Service. 1973. Threatened wildlife of the 

United States. U.S. Fish Wildl. Serv., Resour. Publ. 114. 



39 



289 pp. 

U.S. Fish and Wildlife Service. 1978. Status of native species pro- 
tected by the endangered species convention. Federal Register 
43(86):19176-19191. 

Van Tyne, J., and G. M. Sutton. 1937. The birds of Brewster 
County, Texas. Univ. Mich. Mus. Zool. Misc. Publ. 37. 

Wauer, R. H. 1973. Birds of Big Bend National Park and vicin- 
itv. University of Texas Press, Austin. 233 pp. 

West, S. 1979. ABA's most-wanted birds. Birding ll(2):54-64. 

Willard, F. C. 1910. Seen on a dav's outing in southern Arizona. 
Condor 12(3): 110. 



Osprey (Pandion haliaetus carolinensis Gmelin) 

Status: Severe declines, especially on the East Coast. 
Productivity has been recovering and, in many instances, 
populations stabilizing following the DDT ban in the 
United States. Populations in northwest United States 
have been increasing with artificial water impound- 
ments. Primary threat is continued use of organochlorine 
biocides in Central and South America. 

Original Discovery and Description: Falco carolinensis 
Gmelin, Syst. Nat., vol. 1, pt. 1, 1788, p. 263. Based 
mainly on the fishing hawk, Accipiter piscatorius Catesby 
Carolina, vol. 1, p. 2, plate 2 (in America-South Caro- 
lina). American Ornithologists' Union 1957. 

Background: There is some indication (Ogden 1977a: 
149-151) that Florida ospreys are intermediate in form 
between P. h. carolinensis and P. h. ridgwayi, which in- 
habits the Bahamas, Yucatan, British Honduras, and pos- 
sibly Cuba (Brown and Amadon 1968). 

The osprey, a large raptor of worldwide distribution, 
feeds on live fish, often diving beneath the water's surface 
to capture its prey. Becent major declines have been 
attributed primarily to eggshell thinning caused by envi- 
ronmental contaminants (Henny 1977a). 

Status Determination: On the Blue List, an "early 
warning" list of species exhibiting potentially serious de- 
clines, since 1971 (see December issues of American Birds, 
1971 to present). Classified as Status Undetermined by 
the U.S. Fish and Wildlife Service (1973). Godfrey (1970) 
classified the osprey as endangered in Canada. 

Description: The osprey is a large raptor, appearing 
intermediate in size between large buteonine hawks and 
eagles. Ospreys are white underneath with brownish- 
black wristmarks, buff to brown speckles in the breast, 
and brown to brownish-black above. Head is white with 
a thick, brownish-black eyestripe. Cere and feet are blue- 
gray. In flight it can often be distinguished by the black 
wristmarks and the definite crook in the wings (see Peter- 
son 1947). 

Juvenile ospreys have orangish-red to dark brownish- 
yellow irides and buffy feather edging on the back. Adults 
have yellow irides and lack the buffy feather edges on the 



back. Males typically are less extensively marked on the 
breast (Peterson 1947; Friedmann 1950; Brown and 
Amadon 1968). 

The large nests placed at the top of trees (usually dead) 
are unique and are used in locating osprey territories 
during air and ground searches (Mathisen 1968&). 

See Brown and Amadon (1968) and birding guides for 
characteristics for identification of parts or products. 

Distribution: Breeds north to northwestern Alaska and 
central Canada; south to southern United States, the 
Sonoran coast, and Baja California. Winters from the 
southern United States south as far as Chile and Argen- 
tina. Non-breeding subadult birds (1-year-olds) remain 
on the wintering grounds through the northern summer 
(AOU 1957; Henny and Van Velzen 1972). (See range 
map in Henny (1977a:200) for areas of breeding concen- 
trations.) 

Habitat: The osprey, a fish-eating bird, is typically asso- 
ciated with water. Significant nesting populations are 
found in coastal areas and in regions with an abundance 
of lakes (Henny 1977a). 

Fishing sucess appears to be greatest in areas of rela- 
tively shallow water. Shallow areas in lakes and rivers, 
floodings, and intertidal areas are favored (D. S. Mac- 
Carter 1972; Ueoka and Koplin 1973). Nesting habitat is 
fairly specific: dead or open-topped live trees are favored 
in natural situations. Nests are invariably placed at the 
very top of the tree. Ospreys are very adaptable to artifi- 
cial nesting structures, nesting commonly on old duck 
blinds, channel markers, telephone poles, and a variety of 
other man-made structures (Mathisen 1968&; Beese 1970; 
French 1972; D. L. MacCarter 1972; Ogden 1977a). 
Nesting platforms erected specifically for ospreys have 
been very successful (Postupalsky and Stackpole 1974; 
Bhodes 1977). Ospreys usually nest close to water; how- 
ever, lack of suitable nest sites in some areas apparently 
results in nesting as far as several kilometers from the 
nearest body of water 'Postupalsky 1977fo). 

Banding recoveries indicate that 1 -year-old birds re- 
main on the wintering grounds during their first summer. 
Two-year-old birds return to the United States and an 
estimated 25-54% return to their natal areas (Henny and 
Van Velzen 1972). 

Critical Habitat: Decreasing availability of suitable nest- 
ing trees due to forestry practices, drainage, weather 
damage, and human disturbance. Beduced feeding habi- 
tat due to recreational use of lakes and reduced fisheries 
due to acid rain. Lakes with high sensitivity to acid rain 
are generally found in northern California, Oregon, 
Washington, northern Idaho, Montana, northeastern 
Minnesota, northern Wisconsin and Michigan, and east 
of the Appalachians (U.S. Environmental Protection 
Agency 1979). 

Feeding Habits: Ospreys prey almost exclusively on live 



40 



fish; dead fish are occasionally taken (Dunstan 1974). 
There are several scattered reports of non-fish prey, in- 
cluding carrion (Miller 1923; Petrovic 1972; Wiley and 
Lohrer 1973; Hosford 1974; Kern 1976; Proctor 1977; 
Thorpe and Boddam-Whetham 1977). 

Dunstan (1974) described several types of fishing 
behavior in Minnesota. Ospreys soared 10-60 m over the 
water, hovering briefly, or perched in trees along the 
shoreline while searching for fish. They also dragged their 
feet in the water for short distances, especially over weed- 
beds, ostensibly to startle fish into movement. Grubb 
(1977a) found that capture rate and number of dives were 
significantly less under cloudy skies or when wind rippled 
the water surface, apparently due to reduced visibility. 
Under cloudy, windy conditions the energy expended per 
prey capture may be six times greater than under calm, 
sunny conditions. Visibility also appears to be affected by 
the prey's movement relative to the water surface; osprey 
dives from a hover have been found to be 50 % more suc- 
cessful than dives from a glide, or "interhover" (Grubb 
19776). Osprey dive into the water and seize the fish, 
often completely submerging beneath the water's surface. 
Captured fish are aligned head-first to the direction of 
travel, presumably decreasing air resistance (D. S. Mac- 
Carter 1972). 

Litde is known about feeding habits on the wintering 
grounds. Ueoka and Koplin (1973) described changes in 
success rates as the breeding season progressed and also 
changes in success rates during different stages of the tidal 
cycle. 

Reproduction and Development: Courtship activities and 
egg-laying typically begin in late spring, shordy after the 
ice is out on inland lakes, in the northern United States 
and Canada. Southern populations are less synchronous. 
Egg-laying in Florida ranges from late November to 
March; the peak is in December and January (Ogden 
1977a). In northwestern Baja California egg-laying be- 
gins in January and continues through March (Jehl 1977). 
Nests are constructed, of dead sticks, grasses, mosses and 
lichens, and miscellaneous materials (Bent 1937; 
Mathisen 19686; D. L. MacCarter 1972; Garber 19726; 
Beebe 1974; Stinson 1976c). Nesting materials are 
brought to the nest primarily by the male (Brown and 
Amadon 1968; Garber 19726). Nest-building and defense 
of the nesting territory are carried out by the female 
(Garber 19726). 

Ospreys perform noisy courtship displays, one con- 
sisting of steep dives by the male, often in pursuit of the 
female, and the other a slow, hovering flight (Beebe 
1974). Copulation takes place on or near the nest (Bent 
1937). Clutches of three eggs are normally laid; incuba- 
tion lasts about 38 days (Garber and Koplin 1972). Incu- 
bation is shared by both sexes; the male incubates about 
30% of daylight hours (Garber 19726; Garber and Kop- 
lin 1972). Food is provided by the male during incubation 
and early nesting stages. When the young no longer re- 



quire constant brooding (5-6 weeks), the female also 
hunts (Garber 19726; D. S. MacCarter 1972). 

Garber (19726) found that young were sheltered from 
excessive sun, rain, and wind until they were about 7 
weeks old; the female then perched nearby, although 
young were still brooded at night. Young ospreys fledge at 
44-59 days of age (Stotts and Henny 1975; Stinson 
1977a). In Virginia, Stinson (1977a) found the young to 
be dependent on their parents for at least 6 weeks after 
fledging, although this may be considerably shorter at 
higher altitudes and more northern latitudes (Beebe 1974; 
Henny 19776). 

Ogden (1977a) reported that Florida ospreys do not mi- 
grate, dispersing only short distances northward during 
the non-breeding season. Ospreys from the northern 
United States and Canada spend the winter in Panama, 
the West Indies, and South America (Henny and Van 
Velzen 1972). Young of the year spend at least 16 contin- 
uous months in the tropics and do not return north until 
they are 2 years old. Of these, 28-54% return to their 
natal area (Henny 1977a) and 5-10% may go through the 
motions of nesting, or "keeping house." Breeding has not 
been documented for 2-year-olds and such attempts can- 
not be counted in assessing reproductivity of the popula- 
tion (Henny and Van Velzen 1972). Most ospreys begin 
breeding at 3 years of age although some may not attempt 
breeding until age 4 (Ogden 1977a), and sometimes not 
until age 6 (S. Postupalsky, personal communication). 
Little is known about the length of sexual activity and 
life-span of the osprey although life tables derived from 
band recoveries (Henny and Wight 1969) indicate a life- 
span of 15-20 years. They estimated a first-year mortality 
at 51.5-57.3%, and 16.2-19.6% each year thereafter. 

Various State and Federal agencies conduct annual re- 
production surveys — see Henny (1977a) and Ogden 
(19776). 

Diseases and Parasites: Little published information is 
available concerning diseases and parasites of the osprey. 

Predators and Other Mortality Factors: Predation occurs 
primarily during the egg and early nestling stages of the 
osprey. Gulls are normally repelled from the nest, even in 
the presence of human observers, but in extreme situa- 
tions may cause some losses of eggs or small young (Ames 
and Mersereau 1964; Garber 19726). Although inter- 
specific aggression occurs frequently between ospreys and 
bald eagles, actual predation appears to be infrequent 
(Ogden 1975). Raccoon predation may become locally se- 
vere in some instances but normally appears not to be a 
serious factor (Reese 19776). Most investigators consider 
predation to be minimal on their study areas (Ames and 
Mersereau 1964; Garber 19726; D. L. MacCarter 1972). 
Organochlorine pesticides, notably DDT and its deriva- 
tives, are primarily responsible for recent declines of the 
osprey (Ames and Mersereau 1964; Ames 1966; Keith 
1966; Anderson and Hickey 1972; Henny 1972; Johnson 



41 



et al. 1975; Wiemeyer et al. 1975; Grier et al. 1977; 
Henny 1977a; Spitzer et al. 1977). Eggshell thinning and 
resulting poor productivity have been associated with 
high concentrations of DDE (Spitzer et al. 1977). It ap- 
pears that eggshell thinning greater than 15-20% is asso- 
ciated with reproductive difficulties (Henny 1977a). In 
addition, high concentrations of PCB's and heavy metals 
(mercury and lead) have been associated with increased 
embryonic mortality in other species (Wiemeyer et al. 
1972). Locally severe weather, hurricanes (Wiemeyer et 
al. 1975), and illegal shooting contribute to mortality but 
have not had a major impact on osprey populations. Ille- 
gal shooting pressure appears to be declining in the 
United States as a result of increasing public awareness of 
raptorial species and increased law enforcement. Major 
causes of mortality in a group of 33 ospreys recovered 
from 1964 to 1973 were impact injuries, emaciation, 
shooting, and respiratory infections (Wiemeyer et al. 
1980). 

Population Level: Henny (1977a) discussed United States 
osprey populations on a regional basis. 

North Atlantic Coast. — Osprey declines were first 
noted in this region; the population is probably less than 
10% of its former size. The osprey populations of Con- 
necticut, Rhode Island, and Gardiner's Island declined at 
a rate of 6.5% for 1945-60, 14.4% for 1961-65, 14.3% 
for 1966-70, and 4.0% for 1971-75. Productivity should 
continue to improve as long as persistent pollutants are 
not used. 

South Atlantic Coast. — This region probably has the 
highest breeding concentrations in the world. More than 
two-thirds of the birds nest on man-made structures 
(channel markers, duck blinds, and artificial nest plat- 
forms). Most populations are at normal or slightly below 
normal rates of productivity. 

Great Lakes Region. — Ospreys showed declines similar 
to the North Atlantic Region in the 1950's and 1960's. Re- 
cent production appears to be normal or nearly so and 
populations more or less stabilized. 

Western North America. — Little historical data are 
available on declines and extent of osprey populations. 
Production has been normal in most areas except in Yel- 
lowstone Park, where human disturbance may be a fac- 
tor. Osprey populations have increased in the last two 
decades in northern Idaho and northeastern Washington. 
Present populations, nesting on relatively new man-made 
reservoirs, may be greater than in historic times. 

Southern Region. — Florida and Mexican populations 
are non-migratory and may have mortality and recruit- 
ment rates differing from northern populations; however, 
present production appears adequate in terms of recruit- 
ment rates of northern populations. 

Spitzer et al. (1978) reported that productivity in the 
Connecticut-Long Island area had increased to 1.2 young 
fledged per pair in 1976-77, which approaches pre-DDT 
levels of productivity. This increase coincides with a de- 



crease in DDE and dieldrin residues in unhatched osprey 
eggs. Such increases in productivity, following the DDT 
ban, appear to be typical of North American osprey pop- 
ulations (Henny and Anderson 1979). 

Thacker (1971) estimated three ospreys held in captiv- 
ity (zoos). Captive breeding potential is unknown. 

Reasons for Current Status: Although traditional habitat 
of tree-nesting ospreys is disappearing in many areas, 
ospreys are adaptable to nesting on man-made structures 
such as duck blinds, channel markers, and man-made 
platforms and do not appear seriously affected by this 
loss. In Chesapeake Bay, only one-third of nesting ospreys 
were using trees (Henny et al. 1974) and the trend toward 
man-made nest sites continues along the entire mid-At- 
lantic coast (Henny et al. 1977). 

Persistent pollutants, notably DDE, have been primar- 
ily responsible for declines of osprey populations (Henny 
1977a). Productivity in most populations has been in- 
creasing since the decrease and eventual banning of DDT 
use in the United States (Henny 1977a). 

Management Activities: Osprey management areas are 
being implemented, especially in the western United 
States where osprey concentrations are on State or Fed- 
eral land. Management plans consider human and man- 
agement activities in nesting areas, preservation and con- 
struction of nest sites, reproductive surveys, and manage- 
ment of non-game fish (Henny 1977a). 

The ability of ospreys to adapt to artificial nesting sites 
has encouraged the erection of nesting platforms by the 
U.S. Forest Service, State agencies, and private citizens 
(Reese 1970; Rhodes 1972, 1977; Henny 1977a; Postupal- 
sky 19772?) . Aerial surveys along the Atlantic coast have 
shown nesting platforms in use from New York to South 
Carolina (Henny 1977a). In some areas nesting success 
may be higher for birds on nesting platforms than in trees 
(Henny et al. 1974). 

Readers are referred to Ogden (1977fc) and Henny 
(1977a) for recent research activities and overall status of 
the osprey. 

Ospreys are protected under the United States-Mexico 
Migratory Bird Treaty of 10 March 1972. 



References and Selected Bibliography 

Abbott, C. C. 1911. The home-life of the osprey. Witherby and 
Co., London. 54 pp. 

Allen, C. S. 1892. Breeding habits of the fish hawk on Plum Is- 
land, New York. Auk 9(4):313-321. 

American Ornithologists' Union. 1957. Check-list of North 
American birds. American Ornithologists' Union, Baltimore, 
Md. 691 pp. 

Ames, P. L. 1964a. Notes on the breeding behavior of the osprey. 
Atl. Nat. 16(l):26-33. 

Ames, P. L. 1964£>. Experiments in the artificial incubation of 
osprey eggs. Peabody Museum of Natural History, New Ha- 
ven, Connecticut. (Unpubl. rep.) 



42 



Ames, P. L. 1966. DDT residues in the eggs of the osprey in the 
northeastern United States and their relation to nesting suc- 
cess. J. Appl. Ecol. 3(Suppl.):87-97. 

Ames, P. L., and G. Mersereau. 1964. Some factors in the de- 
cline of the osprey in Connecticut. Auk 81(2):173-185. 

Anderson, D. W., and J. J. Hickey. 1972. Eggshell changes in 
certain North American birds. Proc. Int. Ornithol. Congr. 14: 
514-540. 

Anonymous. 1881. A fish hawk's nest in a channel buoy. Sci. 
Am. 45 (Sept. 10). 

Anonymous. 1972. Ospreys in the Gulf of California. Pages 
45-46 in V. T. Harris, compiler. Wildlife Research 1971. 
U.S. Fish Wildl. Serv., Resour. Publ. 111. 106 pp. 

Arbib, R. S., Jr. 1973. The Blue List for 1974. Am. Birds 27(6): 
943-945. 

Arbib, R. S., Jr. 1975. Blue List of 1976. Am. Birds 29(6): 
1067-1971. 

Bahr, P. H. 1907. A study of the home life of the osprey. Br. 
Birds 1:17-22, 40-43. 

Bates, B. 1939. Notes on the osprey (Pandion haliaetus caroli- 
nensis). Yellowstone Nature Notes 16:42^44. 

Beckett, T. A., III. 1970. Nesting of the osprey near George- 
town, S.C. Chat 34(3):80-81. 

Beebe, F. L. 1974. Field studies of the Falconiformes of British 
Columbia. Occas. Pap. B.C. Prov. Mus. 17. 163 pp. 

Bent. A. C. 1937. Life histories of North American birds of 
prey. Part 1. U.S. Natl. Mus. Bull. 167. 409 pp. 

Berger, D. D., and H. C. Mueller. 1969. Ospreys in northern 
Wisconsin. Pages 340-341 in J. J. Hickey, ed. Peregrine falcon 
populations: their biology and decline. University of Wiscon- 
sin Press, Madison. 596 pp. 

Berger, G. 1957. Bemerkungen zur Haltung eines Fischadlers 
(Pandion haliaetus L.). Zool. Gart. 23:250-251. 

Berger, G. 1964. Weiterer Beitrag zur Haltung des Fischadlers 
(Pandion haliaetus L.). Zool. Gart. 29(4):188-189. 

Brady, F. H. 1939. Notes on the osprey (Pandion haliaetus carol- 
inensis). Yellowstone Nat. Notes 16:40. 

Brown, L. 1976. British birds of prey. Collins, London. 400 pp. 

Brown, L., and D. Amadon. 1968. Eagles, hawks, and falcons 
of the world. McGraw-Hill, New York. 2 vols. 945 pp. 

Brown, W. H. 1953. Unusual behavior of an osprev. Wilson 
Bull. 65(2):116. 

Burr, F. F. 1912. Note on the bald eagle and osprey. Auk 29(3): 
393. 

Carrier, W. D., and W. E. Melquist. 1976. The use of rotor- 
winged aircraft in conducting nesting surveys of ospreys in 
northern Idaho. Raptor Res. 10(3):77-83. 

Chancellor, R. D., editor. 1977. World conference on birds of 
prey. International Council for Bird Preservation (ICBP). 
Taylor and Francis, Ltd., London. 442 pp. 

Chapman, F. M. 1908a. The fish hawks of Gardiner's Island. 
Bird-Lore 10(4): 153-159. 

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46 



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Peregrine Falcon (Falco peregrinus Tunstall) 

Status: 

American peregrine jalcon. —Endangered; restocking 
of vacated range with other forms appears feasible with 
the ban on United States use of DDT. 

Arctic peregrine jalcon. — Endangered; continued and 
increasing use of organochlorine biocides in Central and 
South America spells an uncertain future for this subspe- 
cies. 

Peale's falcon. — Stable. 

Original Discovery and Description: American peregrine 
falcon (F. p. anatum Bonaparte): Falco anatum Bona- 
parte, Geogr. and Comp. List, 1838, p. 4. New name for 
Falco peregrinus Wilson, Am. Ornithol. vol. 9, 1814, p. 
120, plate 76 (Egg Harbor, New Jersey). American Orni- 
thologists' Union 1957. 

Arctic peregrine falcon (F. p. tundrius White, new sub- 
species): Type — adult male, No. 46581 National Museum 
of Canada, near northwestern Sherman Basin, Adelaide 
Peninsula, Northwest Territories, Canada. 15 August 
1957 (White 1968fc). 

Peale's falcon (F. p. pealei Bidgway): Falco communis 
var. Pealei Bidgway, Bull. Essex Inst., 5, no. 12, Dec. 
1873 (Feb. 1874), p. 201 (Oregon to Sitka-Oregon). AOU 
1957. 

Background: In a recent biosystematic study of the pere- 
grine falcon. White (1968fo) separated F. p. tundrius as a 
new subspecies from F. p. anatum. Tundrius is not yet of- 
ficially recognized by the American Ornithologists' Union 
(1973, 1976). Tundrius is currently recognized as breed- 
ing in the tundra biome and anatum as south of the tun- 
dra biome. 

The peregrine falcon is of great ecological significance, 
because it is the focal point of inquiries into the effects of 
DDT and other contaminants on the environment. F. p. 
anatum has been extirpated from the eastern portions of 
its range and is doing very poorly in the western United 
States and Canada. F. p. tundrius is also doing poorly as a 
result of increasing pesticide use in Central and South 
America where the falcons winter. F. p. pealei appears to 
be maintaining its population. The peregrine represents 
one of man's more concentrated efforts in the restoration 
of breeding populations in its range. Intensive field 
studies and captive propagation are now being carried 
out toward these ends. 

Status Determination: F. p. tundrius and F. p. anatum 
are on the U.S. Department of the Interior Endangered 
List (U.S. Fish and Wildlife Service 1970a, 1970fo, 1973). 
F. p. anatum is considered as Endangered by the Interna- 
tional Union for Conservation of Nature and Natural Be- 
sources (1969) and in Canada (Godfrey 1970). These 
listings were made shortly after White's (1968fc) separ- 
ation of F. p. tundrius and could include tundrius. 



48 



Description: Peregrines are large falcons with long, 
pointed wings and a moderately long tail. Females 
average 1.6 times heavier than males. In general, adults 
are slate gray to bluish gray with black head and a black- 
ish malar stripe. Underneath they are pinkish to dark 
rufous with blackish spotting and barring. Immature 
peregrines are more brownish above with whitish or buff 
feather edges. Underneath they are buffy and have dark 
streaks. The malar stripes are less well defined and light- 
colored immature arctic peregrine falcons have a broken 
malar stripe, with a light break extending from the corner 
of the mouth (Beebe and Webster 1964; Brown and 
Amadon 1968; White 1968b). 

Anatum peregrines vary in size and color from east to 
west and from north to south. The population formerly 
breeding in the eastern United States tended to be darker, 
to plumbeous black above, whereas birds in the western 
United States tend to have a brownish, more rufous, cast. 
Northern birds tend to be lighter above and less exten- 
sively barred underneath. They appear to be short-to 
medium-range migrants, in contrast to the more southern 
populations, which are primarily resident year-round. 
Tundrius peregrines, which occupy the tundra biome of 
North America, are highly migratory and exhibit "leap- 
frog" migration, passing over the more resident anatum 
populations and extending during winter into Central 
and South America. They are smaller, paler above, and 
lack the rufous underparts of anatum birds. Peale's fal- 
con, which occupies the Pacific Coastal islands and the 
Aleutians, is larger and darker than American and arctic 
peregrines (White 1968b). 

Locations of eyries and perching places are often re- 
vealed by the streaks of white droppings below perches. 

See Beebe and Webster (1964:114), Brown and 
Amadon (1968); White (1968b), and birding guides for 
characteristics for identification of parts or products. 

Distribution: Breeding range of the American peregrine 
falcon extends northward across Canada and Alaska 
about to tree line where it intergrades with the Arctic 
peregrine. It extends south to 23° N latitude in Baja 
California, east to Tamaulipas, Mexico (Cade 1975; Fyfe 
et al. 1976), southwestern Texas, Kansas, Arkansas, Mis- 
souri, Tennessee, southern Illinois, Indiana, Pennsyl- 
vania, New Jersey, and in the Appalachian Mountains 
through Virginia to eastern Tennessee and to South Caro- 
lina and Georgia (Bent 1938; Friedmann 1950; AOU 
1957; White 1968b). Southern populations of the Ameri- 
can peregrine are primarily resident during winter range, 
whereas northern populations are short- to medium- 
range migrants, wintering in the southern United States 
and into Central America. The now extirpated eastern 
population tended to move to the eastern coastal regions 
during the winter. 

The Arctic peregrine falcon breeds north of the tree 
line in Alaska, Canada, and Greenland to about 77° N 
latitude. It winters from the United States Culf Coast and 



Baja California south to 40° S latitude in Chile and prob- 
ably 35° S latitude in Argentina (White 1968b). 

Peale's falcon is primarily a permanent resident of the 
Queen Charlotte and other Pacific Coast Islands; its 
range extends northward through the Aleutian Islands 
(White et al. 1971). Some wintering individuals are ob- 
served inland on the Pacific Coast (AOU 1957). 

The American peregrine falcon was extirpated in the 
eastern and middle United States and southern Canada. 
Scattered areas of breeding remain in the western United 
States and Mexico, notably in Idaho, Colorado, Arizona, 
and Chihuahua. A few scattered pairs remain in northern 
Alberta, northern Canada, and the forested regions of 
Alaska (Fyfeet al. 1976). 

Present range of arctic and Peale's falcon is essentially 
the same as its former range, although substantial de- 
clines of arctic populations have occurred in the last 5-10 
years (Fyfe et al. 1976). 

Habitat: Breeding American and Peale's falcons are typi- 
cally associated with tall cliffs, which provide sanctuary 
from disturbances, and ledges, potholes, or small caves 
suitable for constructing the nest scrape. Arctic peregrines 
utilize a variety of nest sites from slopes, cutbanks, and 
cliffs on northern rivers to shoreline cliffs and seastacks 
(Cade 1960; Hickey and Anderson 1969; White and Cade 
1971). Old stick nests of ravens and rough-legged hawks 
constructed on river slopes and cutbanks often provide a 
more stable nest site and are frequently utilized (Cade 
1960). Winter habitat requirements are less specific than 
breeding habitat. Areas that provide abundance of prey 
and are relatively free of pollutants are the most im- 
portant. 

Nest sites are typically located near lakes, rivers, or 
marshes where prey species are more abundant and vul- 
nerable. Accordingly, areas providing suitable prey and 
cliffs or other nesting habitat are the most important. 
Peregrines occasionally nest on various man-made struc- 
tures, even within large cities (Groskin 1947, 1952; Hall 
1970), and a remnant population nested in holes and 
broken-off stubs of giant trees before the 1940's in the 
Mississippi Valley (Hickey 1942). In more northern re- 
gions, cutbanks and gravel slopes associated with rivers 
replace cliffs as nesting areas. Due to the ephemeral na- 
ture of this type of nesting situation, historical occupancy 
is not characteristic of most northern sites as it is with the 
southern cliffs. 

The more migratory northern populations encounter a 
wide variety of habitat types while on migration. Mi- 
grating peregrines tend to follow closely Great Lakes, 
coastal, and barrier beach shorelines. In general, areas 
with adequate prey populations are selected for winter- 
ing. 

Critical Habitat: Entire breeding range of American and 
arctic peregrines where suitable nest sites are available. 
Assessment of historical sites to determine suitability for 



49 



reintroduction of stock produced in captivity is currently 
under way. Habitat of Peale's falcon appears relatively 
undisturbed at the present time. 

Feeding Habits: Although a wide variety of prey species 
have been recorded, peregrines feed almost entirely on 
birds. Medium-sized passerines, icterids, shorebirds, 
pigeons, and small to medium-sized waterfowl form the 
bulk of their diet. Rarely, mammals and even fish have 
been recorded (Bent 1938; Cade 1960; White and Cade 
1971). 

The peregrine falcon shows an impressive display of 
speed and power when pursuing prey, whether in direct 
pursuit or in swift dives from above (Hickey and Ander- 
son 1969). It has been estimated that peregrines attain 
speeds of 242-312 km/h when stooping on prey; more re- 
cent evidence indicates that up to 443 km/h may be at- 
tained (Brown and Amadon 1968). It might be noted that 
man, in free fall, reaches a terminal speed of about 
193 km/h. 

Prey pursuit may be initiated from a perch or while 
soaring at great heights. Small to medium-sized birds are 
usually captured directly; birds too large to be carried are 
knocked to the ground by one or more stoops and then 
killed by severing the neck vertebrae with the sharply 
notched beak. Cochran (1975) gave a good account of 
hunting behavior during migration. 

Seasonal food habits reflect seasonal and geographical 
distribution and availability of prey species, and seasonal 
distribution of peregrines. For example, breeding water- 
fowl and shorebirds would be more available to northern 
populations whereas passerines, starlings, and pigeons 
might be more available to wintering and southern breed- 
ing populations. 

Reproduction and Development: Peregrines lay their eggs 
in shallow depressions scraped in the gravel and debris on 
the nesting ledge. Eggs are typically laid in late March 
and April in the United States and southern Canada and 
into June in the far north (Hickey 1942; Cade 1960). 

The male is typically the first to arrive at the nesting 
cliff in the spring. Mates are attracted to the cliff and to 
aerial displays of the resident birds. Although the male 
and female investigate various ledges together, the female 
makes the final selection for the nest scrape. Eggs are in- 
cubated (about 33 days) primarily by the female. Average 
clutch size varies from 2.9 to 3.7, being highest in the 
mid-latitudes and lowest in the far north (Hickey and 
Anderson 1969). 

The male provides all the food and relieves the incu- 
bating female for short periods of time while she eats. 
After the eggs hatch, the female remains closely attached 
to the eyrie until the young are 2-3 weeks old, at which 
time she begins to supply additional food for the rapidly 
growing young. If the first clutch is destroyed, a second 
clutch is frequently laid about 2 weeks later; it is usually 
smaller than the first clutch. However, the very short 



breeding season in the far north precludes any renesting 
in the event of destroyed first clutches; even late-nesting 
birds may not have enough time to fledge their young in 
some years. 

Peregrines are covered with short whitish down after 
hatching and feathers appear at about 2 weeks of age. 
The young fledge at 5-6 weeks of age. They gradually be- 
come independent of their parents as their power of flight 
improves and they are able to kill on their own. In the far 
north, peregrines may fledge as late as early September, 
and with migration beginning as early as mid-September, 
the fledged young must quickly learn to kill for them- 
selves. 

Peregrines usually begin breeding when they are 2 to 3 
years old although breeding 1 -year-olds have been 
observed (Fyfe 1976a). The maximum life-span is gener- 
ally believed to be about 20 years in the wild (Enderson 
1969c; Young 1969). Enderson (1969c) estimated imma- 
ture mortality to be 70% and the average annual adult 
mortality to be 25 % . The effects of senescence upon re- 
productive efficiency is unknown, although a female 
known to be at least 19 vears old raised two voung (Hall 
1970). 

Diseases and Parasites: Peregrines may contract a consid- 
erable number of diseases, none of which are considered 
to have a great effect on peregrine populations. However, 
on a local scale, botulism, myiasis, and trichomonas are 
known to have caused considerable mortality (White 
1963; Trainer 1969; Stabler 1969; Porter et al. 1973). In- 
clusion body disease, a herpesvirus infection, has caused 
death in captive peregrines (Graham et al. 1975). 

Predators and Other Mortality Factors: Mammalian 
predators, including raccoons, bobcats, fox, striped 
skunks, ringtails, and opossums are known to rob nests of 
eggs and small young. Great horned owls may prey on 
nestlings and recently fledged young (White and Lloyd 
1962; Porter et al. 1973:45). Cade (1960) listed timber 
wolf, red fox, arctic ground squirrel, and golden eagle as 
the most important predators in northern Alaska. 

Organochlorine pesticides, notably DDT and its 
metabolites, are primarily responsible for the cata- 
strophic decline of the peregrine. Heavy metals, mostly 
mercury and lead, have been implicated in increased em- 
bryonic mortality. Other chemicals known to be detri- 
mental to reproductive success include aldrin, dieldrin, 
and PCB's (Jefferies and Prestt 1966; Cade et al. 1968, 
1971; Enderson et al. 1968; Enderson and Berger 1968; 
Hickey and Anderson 1968; Hickey 1969; Lincer et al. 
1970; Ratcliffe 1970; Risebrough et al. 1970; Bogan and 
Mitchell 1973; Walker et al. 1973; White et al. 1973; 
Clement 1974; Peakall et al. 1975). Illegal shooting by ir- 
responsible hunters is still a considerable source of mortal- 
ity. Inexperienced juvenile birds are more susceptible 
than adults. Of a selected sample of peregrine band re- 
turns, 50% of the immatures and 33% of the adults had 



50 



been shot (Enderson 1969c). 

Severe weather conditions may also cause considerable 
mortality at various stages of the life cycle, especially in 
the far north. Ruos (1970) found a significant correlation 
between number of migrating peregrines (primarily arc- 
tic) on the east coast and daily minimum temperatures in 
the Arctic. Various accidents such as young falling from 
the nest ledge, rocks falling on the nest ledge, and young 
hitting wires or automobiles contribute to mortality 
(Cade 1960; Cade and Fyfe 1970:242; White and Cade 
1971; Burnham et al. 1974; Mattox 1975). 

Population Level: 

American peregrine falcon. —Extirpated in the middle 
and eastern United States and Canada. Fyfe et al. (1976) 
reported only 62 occupied sites in the western United 
States and adjacent Mexico. In Alberta only 4 of the 48 
known sites showed any activity. In the western 
Canadian boreal forest, declines of 50 % or more have oc- 
curred. It is estimated that less than 200 pairs of pere- 
grines attempted to nest in the forested regions of Alaska 
(Fyfe et al. 1976). 

Arctic peregrine falcon. — Although historical data for 
the Arctic are lacking, it appears that declines of 50% or 
more have occurred. As yet, complete extirpation of any 
region has not been documented (Fyfe et al. 1976). 

Peale's falcon. — Present populations are essentially the 
same as in historic times (Fyfe et al. 1976). 

Thacker (1971) estimated 116 peregrines held in cap- 
tivity by zoos and for research. The number of peregrines 
held for falconry purposes is unknown; 100-200 is prob- 
ably a reasonable estimate. An additional number are 
held by captive breeding establishments, primarily The 
Peregrine Fund, with facilities at Cornell University, 
Ithaca, New York, and Fort Collins, Colorado, and the 
Canadian Wildlife Service facilities at Edmonton, 
Alberta (Fyfe 1976a; Cade and Dague 1976). Captive 
breeding potential appears very good. 

Reasons for Current Status: The effects of human en- 
croachment and consequent destruction of habitat re- 
duces prey populations and renders nesting sites unsuit- 
able. Agriculture and extensive wetland drainage have 
also reduced prey populations. Mining, general urban 
development, road construction, and recreation (e.g., 
picnicking, rock climbing) are a few of the facets of 
human disturbance that have resulted in eyrie abandon- 
ment (Herbert and Herbert 1969:139; Porter et al. 1973). 
As yet there has been relatively little disturbance of breed- 
ing habitat in the North. However, exploitation of petro- 
leum reserves and the ensuing disturbance of arctic 
wilderness poses a threat to peregrine breeding habitat 
(Cade and Fyfe 1970; Clement 1974). 

Collecting of birds, and particularly eggs, for museum 
and private collections reached considerable proportions 
in the late 1800's and early 1900's. In the 1930's much of 



this activity subsided only to be replaced by removal of 
young for falconry (Herbert and Herbert 1969:135). 
These activities apparently had little effect because major 
declines were not observed during this period. Capture of 
migrating arctic peregrines for falconry is similarly 
thought to have had little effect on populations (Hickey 
1969). 

Eggshell thinning caused by DDT is the primary factor 
believed responsible for peregrine declines. American 
peregrine populations have been completely exterminated 
in the eastern and middle United States and lower 
Canada and are on the verge of extirpation in the western 
United States and Mexico. Declines of 50% or more have 
occurred in the boreal forest regions of Canada and 
Alaska. More recently, in conjunction with increasing 
pesticide use in Central and South America, declines of 
arctic populations have accelerated and in most instances 
less than 50% of the former populations remain. The 
primarily resident Pacific Coast populations (Peale's fal- 
con) appear to be maintaining themselves at the present 
time (Fyfeet al. 1976). 

Recovery Team: Information concerning recovery teams 
and recovery plans in progress may be obtained from the 
Office of Endangered Species, 1000 Glebe Road, Arling- 
ton, Virginia 22203. 

Management Activities: Protection of nesting sites will be 
attempted by publishing only general locations of eyrie 
sites to prevent disturbance and by securing cooperative 
agreements of eyrie site landowners. Upon reoccupation 
of the breeding area by peregrines, actual acquisition will 
be made of the surrounding land. 

In areas where lack of nesting sites is a limiting factor, 
potholes dug into the cliffs have been readily accepted by 
prairie falcons and peregrine falcons (Porter et al. 
1973:60; Cade 1974a:91). 

Protection plans as outlined in Endangered Species 
Peregrine Falcon Recovery Plans involve protection from 
killing, taking, or disturbance by humans or natural 
predators; encouraging public support; and striving for 
wise use of potential environmental pollutants. 

Migration counts are maintained at various hawk- 
watches around the country (see Newsletter of Hawk 
Migration Assoc, of North America). Ward (1976) has or- 
ganized an international color-banding program to aid in 
migration studies. Reproductive success of North Amer- 
ican peregrines is summarized by Fyfe et al. (1976). 

In addition to several relatively small private breeding 
projects (Snow 1972; Clement 1974), a major effort is 
being put forth by several institutions. The most notable 
is that directed by Thomas J. Cade at Cornell University. 
Starting in 1973 with 20 young, they have raised 434 
peregrines through 1979 and reintroduced a total of 211 
young in the East and 131 in the West. About 70% of 
these fledged successfully and reached independence 
(Cade and Dague 1977, 1978, 1979). In 1979 several pairs 



51 



of released birds laid eggs, fertile in at least one nest, but 
hatched no young. There were also eight other sightings 
of individual birds in the East. The reestablishment of 
breeding peregrines in the East appears a certainty (Cade 
and Dague 1979). The Canadian Wildlife Service, under 
the direction of Richard Fyfe, Edmonton, Alberta, is also 
producing a large number of young for reintroduction 
purposes (Cade and Dague 1976). 

References and Selected Bibliography 

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Anderson, D. W., and J. J. Hickey. 1972. Eggshell changes in 
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52 



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53 



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57 



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Prairie Falcon (Falco mexicanm Schlegel) 

Status: Prairie falcon populations appear stable; some 
local declines due to habitat loss have been offset by in- 
creases in other areas. Available habitat appears to be at 
maximum earning capacity in some areas. 

Original Discovery and Description: Falco mexicanus 
Schlegel, Abh. Zool. Vergl. Anat., Heft 3, 1851, p. 15 
(Mexico). American Ornithologists' Union 1957 



58 



Background: The prairie falcon is a large falcon in- 
habiting the western United States, southern Canada, 
and northern Mexico. No close relatives occur in North 
America. Although some local declines have been noted, 
it has held its own in most areas and appears to have 
taken over some areas vacated by declining peregrine fal- 
con populations. Harvesting of prairie falcons for fal- 
conry has increased with the unavailability of peregrines 
for this purpose. 

Status Determination: Listed as Threatened by the U.S. 
Fish and Wildlife Service (1973). Has been on the Blue 
List, an "early warning" list of species exhibiting poten- 
tially serious declines, since 1971 (see December issues of 
American Birds, 1971 to present). 

On Canada's list of endangered birds (Godfrey 1970). 
Fyfe (1977) reported that prairie falcon populations were 
stable in Canada. 

Description: The prairie falcon is a large falcon, slightly 
lighter in build than the peregrine. Females average 1.5 
times heavier than males. Brown to sandy brown above, 
with buffy feather edgings. Creamy white underneath 
with brown streaking; adults have barring on the thighs. 
Axillars and upper flanks form a dark triangle visible at 
the base of the underwings in flight (Brown and Amadon 
1968). 

Young prairie falcons tend to be darker above and 
buffy underneath, with lance-shaped streaking on the 
flanks. The buffiness usually bleaches out several months 
after fledging. Cere and legs are bluish to bluish-gray. 
Adults are lighter with triangular barring on the flanks. 
Cere and feet are yellow; the age at which this occurs 
appears to vary. One-year-old birds (still in juvenile 
plumage) in breeding or potential breeding situations 
have yellow feet and cere (Brown and Amadon 1968; 
USFWS Office of Migratory Bird Management, unpub- 
lished data). 

Locations of eyries and perching places are often re- 
vealed by streaks of white droppings below perches. 

See Friedmann (1950), Brown and Amadon (1968), or 
birding guides for characteristics for identification of 
parts or products. 

Distribution: Breeds from central British Columbia, 
southern Alberta and Saskatchewan, and North Dakota 
south to Baja California, formerly to northwestern Mis- 
souri (see range map in Snow 1974). Winters from the 
northern parts of its breeding range south to central 
Mexico and east to the Mississippi River (AOU 1957). 

Habitat: Prairie falcons inhabit relatively arid western re- 
gions. During the breeding seasons they are found in the 
foothills and mountains, which provide cliffs and escarp- 
ments suitable for nest sites. Escarpments associated with 
river systems are also used. Nesting sites are typically asso- 
ciated with open, treeless terrain which accommodates 



their low-level style of hunting. During the non-breeding 
season they leave the higher elevations and migrate to the 
intermontane valleys and Great Plains. 

Breeding areas are generally at those elevations sup- 
porting suitable hunting habitat; the highest recorded 
nest site is 3,688 m in Colorado (Marti and Braun 1975). 
Nest sites with southern or eastern exposure are preferred 
(Enderson 1964; Leedy 1972); however, in southwestern 
Idaho no preference was noted, ostensibly due to milder 
conditions there (Ogden 1973:28). 

There are marked seasonal habitat preferences; winter- 
ing birds are found away from the breeding areas in the 
intermontane valleys and on the Great Plains (Enderson 
1964). Enderson (1964) recognized three distinct popula- 
tion units in terms of seasonal habitat use in Colorado: the 
breeding population, a post-breeding population found 
from June to October, and a wintering population. Age 
ratios of wintering populations appear to vary widely; 
only adults were found wintering on the northern fringe 
of their range (Calgary, Alberta) and only 3 of 22 birds 
caught near Albuquerque, New Mexico, were immature. 
In Colorado, 38% of wintering birds were immature 
(Enderson 1964). In Utah, immature Prairie falcons 
made up 64 to 73% of the wintering population during 
1961-68 (White and Roseneau 1970). 

Critical Habitat: Prey habitat must be preserved and 
breeding areas protected from unauthorized human dis- 
turbance. 

Feeding Habits: Prairie falcons utilize a wide variety of 
foods, including mammals, birds, reptiles, and insects. In 
many areas, mammals, primarily ground squirrels, are 
used extensively during the breeding season (Ogden 1973; 
U.S. Bureau of Land Management 1975). Denton (1975) 
reported both mammal and bird remains at nests. In 
areas lacking ground squirrels, small to medium-sized 
birds and even reptiles (primarily lizards) predominate 
(Bond 1936fo; Ogden 1973; Denton 1975; Kochert and 
Bammann 1975:29-31; Oliphant et al. 1976:367). 
Garrett and Mitchell (1973) reported that small mammal 
control programs in San Joaquin Valley, California, have 
reduced mammalian prey species and appear to have 
reduced nesting densities of prairie falcons; the remaining 
population preys primarily on small passerines. 

Prairie falcons typically hunt from perches and in 
flight, flying at considerable speed. Prey is usually cap- 
tured on or near the ground (Brown and Amadon 1968). 
During the breeding season extra food is cached near the 
nest for subsequent use (Peterson 1976:230). The extent of 
this behavior during the non-breeding season is unknown. 

Recently fledged birds may concentrate on prey less 
difficult to capture, such as reptiles and insects (White 
1962). In Idaho, the main prey species, the Townsend's 
ground squirrel, goes into estivation soon after young 
prairie falcons fledge. The Idaho population leaves the 
breeding areas during this period and presumably prey 



59 



species change considerably at this time (Ogden 1973:36; 
Kochert and Bammann 1975:41). Food habits of post- 
breeding populations are little known; wintering birds 
appear to depend heavily on horned larks in the western 
United States (Enderson 1964; White and Roseneau 1970; 
Garrett and Mitchell 1973:12). 

Reproduction and Development: Reproductive activities 
begin in late winter to early spring (Denton 1975:32). 
Nest sites are typically found in several different situa- 
tions: potholes or larger caves, horizontal ledges, and 
vertical or columnar cracks with lodged material forming 
a suitable nest site. Old nests of ravens, hawks, or eagles 
are sometimes used. Sites with an overhanging ledge af- 
fording protection from the elements are preferred 
(Enderson 1964; Leedy 1972:17; Ogden 1973; Denton 
1975:18). Eggs are laid in shallow depressions scraped in 
the soil and debris. The height of the nest site on the cliff 
varies; generally any nest site over 4.5 m and inaccessible 
to mammalian predators is suitable (Leedy 1972; Ogden 
1973:27). 

Courtship and mate selection occur on the breeding 
grounds and last about a month before egg-laying 
(Enderson 1964; Brown and Amadon 1968). Pairs spend 
long periods of time sitting near the nest site and copulate 
at least several times per day (Enderson 1964:340). Most 
of the incubation, which lasts about 33 days (J. H. Ender- 
son, personal communication), is done by the female. 

Clutches of four or five eggs are typical (Brown and 
Amadon 1968), and if destroyed, a second clutch will be 
laid in 2-3 weeks (Enderson 1964). The male provides all 
the food during incubation, relieving the female while she 
eats, and during the early nestling period. As the young 
grow older and need less attention the female also hunts. 
Nest defense is carried out by both adults; human ob- 
servers have occasionally been struck and their presence 
often provokes attacks on other nesting raptors in the area 
such as barn owls, great horned owls, and red-tailed 
hawks (Dawson 1913; Webster 1944; Enderson 1964:340; 
Ogden 1973:25). 

At hatching, the young are covered with white down, 
which is replaced with juvenal plumage at about 2 weeks. 
Fledging occurs at about 30 days. The post-fledging 
period spent in the natal area is relatively short in those 
areas where ground squirrels are a major food source. 
Dispersal of juveniles (and also adults) is correlated with 
estivation of ground squirrels, which occurs from the end 
of May for adults to mid-July for juveniles (Johnson and 
Melquist 1975:158). In Washington, prairie falcons dis- 
perse to the alpine areas of the Cascade Mountains during 
late summer (Parker 1972). 

Some prairie falcons breed when 1 year old (Webster 
1944), but most probably do not begin breeding until 
their second year (Enderson 1964). Little is known about 
the length of sexual activity. Prairie falcons may live as 
long as 20 years (Enderson 1969fo:506); however, the 
longest known banding recovery is 13 years. Enderson 



estimated immature mortality to be 74 % and average an- 
nual adult mortality to be 25%. Shor (1975) estimated 
the life expectancy of the average falcon as 2.4 years. 

Diseases and Parasites: Several diseases and parasites have 
been reported to cause mortality of prairie falcons, pri- 
marily nestlings. Piatt (1975) attributed the abandon- 
ment of one clutch and the death of seven young in two 
other nests to the presence of the Mexican chicken bug 
(Haemotosephon inodorm). Trichomoniasis or "frounce" 
(Trichomonas gallinae) has affected up to 2% of nesdings 
in some populations (Ogden 1973) and can cause mortal- 
ity of adults. Myiasis, a larval infestation by the nest 
screwworm fly (Calliphoridae), occurs frequently but 
rarely causes mortality (Ogden 1973); however, White 
(1963) attributed the death of 26 dead young in nine nests 
to myiasis. 

Generally, the drier conditions found in prairie falcon 
eyries preclude severe infestations of the nest screwworm 
fly. Oliphant et al. (1976) noted an infestation of ticks 
(Ornithodoros concanesis) in one nest which had severely 
debilitated four of five young and resulted in the death of 
two of the four taken for rehabilitation. The presence of 
lice, mites, ticks, and fleas is apparently a common occur- 
rence in prairie falcon nestlings, but severe debilitation or 
death is rare (Ogden 1973; Oliphant et al. 1976). Ward et 
al. (1970, 1971) noted aspergillosis and inclusion body 
hepatitis in captive prairie falcons, but did not believe 
that either was a significant threat to wild populations. 
Air sac nematodes have been recovered from prairie fal- 
cons (Ward et al. 1970) and have been implicated in sev- 
eral deaths (Bigland et al. 1964; Ward and Fairchild 
1972). 

Predators and Other Mortality Factors: Adult prairie fal- 
cons are little affected by predators, although incubating 
birds could conceivably be taken by great horned owls at 
night. Predation by coyotes, dogs, badgers, bobcats, 
golden eagles, and great horned owls is probably the 
greatest overall factor in nestling mortality by predators 
(Edwards 1973: Ogden 1973; USBLM 1975).' 

Shooting remains the most common cause of mortality 
for prairie falcons (Ogden 1973; Shor 1975). Human dis- 
turbance during the breeding seasons results in abandon- 
ment of nest sites in some areas (Leedy 1972; Edwards 
1973). Various accidents also contribute to mortality. 
Craig and Powers (1976) reported an adult prairie falcon 
that drowned in a stock tank. Falling rock and debris may 
crack or dent eggs, usually resulting in hatching failure 
(Ogden 1973). Human disturbance and improper re- 
search techniques may result in desertion and damage to 
eggs or young (Leedy 1972; Edwards 1973; Fyfe and 
Olendorff 1976). Environmental contaminants are well- 
known causes of mortality and decreased reproduction: 
chlorinated hydrocarbons, notably DDE, result in egg- 
shell thinning and consequent breakage (Fyfe et al. 1969; 
Enderson and Berger 1970; Blus et al. 1972; Enderson 



60 



and Wrege 1973; Ivens and Halliwell 1974). Mercury 
contributes to embryonic mortality (Fimreite et al. 1970) 
although its relationship and the cumulative effects with 
other biocides is not fully understood. 

Population Level: Although most populations are proba- 
bly reduced from historic times, prairie falcons do not ap- 
pear threatened at this time and remain abundant. Gar- 
ret and Mitchell (1973) reported that populations are de- 
clining in portions of California, whereas in other areas 
prairie falcons exhibit successful reproduction and remain 
at levels comparable to historic times. In Colorado, al- 
though production levels appeared relatively low in the 
early 1960's, the population was not deemed to be de- 
clining (Enderson 1964, 1969a). Olendorff and Stoddart 
(1974) believed that current populations in Colorado are 
relatively unchanged from historic times. More recently, 
studies in Washington, Idaho, Colorado, and Montana 
showed higher levels of production and stable or increas- 
ing populations (Leedy 1972; Parker 1973; Ogden 1975; 
Olendorff 1975). The Oregon population appears to be 
stable or increasing; many of the old peregrine sites have 
been taken over by prairie falcons (C. J. Henny, personal 
communication). In Canada, Fyfe (1977) reported de- 
clines during the DDT era and increasing populations 
since then. The inclusion of the prairie falcon on the Blue 
List (see December issue of American Birds. 1971 to 
present) does not appear warranted in light of the above 
studies. 

Thacker (1971) estimated 22 prairie falcons held by 
zoos for research purposes. A considerable number of 
prairie falcons are utilized for falconry (Braun et al. 
1977). A limited example is provided by the U.S. Fish and 
Wildlife Service (1976:Table 16): in California, Colo- 
rado, and Washington, 43 prairie falcons were harvested 
in 1973 and made up 5.8 % of the total number of raptors 
taken for falconry (red-tailed hawks and American kes- 
trels formed the majority) . Prairie falcons are being bred 
successfully in captivity. Captive-raised birds are being 
placed in wild eyries to elucidate techniques for reintro- 
duction of peregrine falcons and a considerable number 
are also being distributed to falconers (Freienmuth 
1976a, 1976£>). About 35 prairie falcons were distributed 
to falconers in 1975 and 1976. Future expansion of this 
program promises to considerably relieve the taking of 
wild birds. 

Reasons for Current Status: It is difficult to determine the 
effects of land-use changes on prairie falcon populations. 
Significant alteration of prey habitat following water im- 
poundment and various agricultural practices 
undoubtedly have had adverse effects. In California, pest 
control eliminated 1 million passerines from 1966 to 
1972; roughly 30% of these were horned larks, a major 
winter prey species (Garret and Mitchell 1973). Habitat 
loss, however, is probably the most important factor 
threatening prairie falcon populations. 



An accurate assessment of the number of prairie falcons 
taken for falconry is available for most States. In Wash- 
ington, falconry harvest has been determined to be well 
within allowable rates. It is estimated that as many as 175 
young could be harvested yearly from the estimated 200 
pairs at current levels of reproduction. Current harvest, 
estimated at 20-30 per year, is substantially below that 
(Parker 1972). The impact of falconry on prairie falcon 
populations is not considered significant at this time nor is 
it expected to be (USFWS 1976). Captive breeding pro- 
grams will undoubtedly become more important in 
reducing the take of birds from wild populations. 

Organochlorine contaminants and mercury appear to 
have been primarily responsible for earlier declines (Fyfe 
et al. 1969, 1976; Enderson and Berger 1970; Enderson 
and Wrege 1973). Restrictions on mercury and DDT use 
have alleviated considerably the declines caused by bio- 
cide pollution (Fyfe 1975, 1977). Local populations in 
areas of agricultural pesticide use continue to show low- 
ered reproduction (Leedy 1972; Parker 1972). In areas 
where prairie falcons feed primarily on birds, productiv- 
ity and nest success are much lower than where the diet is 
primarily mammalian (Fyfe 1972&). 

Management Activities: The most significant step toward 
prairie falcon habitat management was the establishment 
of the Snake River Birds of Prey Natural Area, 12,545 ha 
of prime nesting habitat set aside by the U.S. Department 
of the Interior (USBLM 1975, 1976, 1977; Olendorff and 
Kochert 1977). A moratorium on further agricultural 
development is in effect while habitat requirements of the 
prey utilized by breeding raptors are being studied. 

In many areas, prairie falcons are limited by lack of 
nest sites even though suitable cliffs are present. Nesting 
ledges and holes dug in relatively permanent substrates 
have been widely accepted by prairie falcons in Canada 
(Fyfe and Armbruster 1977). The placement of nesting 
barrels on cliffs subject to erosion could provide much 
additional habitat in the western United States (Olen- 
dorff and Stoddart 1974). 

The Snake River Birds of Prey Natural Area represents 
a large step forward in the study of raptorial species, in- 
cluding the prairie falcon. Project objectives encompass a 
broad program designed to determine requirements in 
terms of habitat, successional stage, food, and space for 
raptor population dynamics, and the effects on raptor 
populations (Kochert and Bammann 1975:vii). 

There are restrictions on mercury and organochlorine 
(primarily DDT) use in United States and Canada. 
Prairie falcons are protected under the United States- 
Mexico Migratory Bird Treaty of 10 March 1972. 

Various reproductive studies have been carried out on 
the Snake River Birds of Prey Natural Area and by 
Richard Fyfe of the Canadian Wildlife Service. 

The Peregrine Fund (facilities at Cornell University, 
Ithaca, New York, and at Fort Collins, Colorado) raised 
prairie falcons on a relatively large scale up to 1978 to 



61 



elucidate techniques for their peregrine reintroduction 
program. The North American Peregrine Foundation and 
a considerable number of private individuals are raising 
prairie falcons for falconry purposes, alleviating pressure 
on wild populations. 

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Tvler. J. G. 1923. Observations on the habits of the prairie fal- 
'con. Condor 25 (3): 90-97. 

U.S. Bureau of Land Management. 1975. Snake River Birds of 
Prey Annual Report. Boise District. Idaho. 193 pp. 

U.S. Bureau of Land Management. 1976. Snake River Birds of 
Prey Annual Report. Boise District. Idaho. 240 pp. 

U.S. Bureau of Land Management. 1977. Snake River Birds of 
Prey Annual Report. Boise District. Idaho. 201 pp. 

U.S. Fish and Wildlife Service. 1973. Threatened wildlife of the 
United States. U.S. Fish Wildl. Sen.. Resour. Publ. 114. 
289 pp. 

U.S. Fish and Wildlife Service. 1976. Environmental assessment: 
proposed falconry regulations. Negative declaration. 61 pp. 

VanTighem, K. 1967. Destruction of the prairie falcon at Cal- 
gary. Alberta. Blue Jay 25(3): 108. 

Walton. B. J. 1978. Peregrine prairie falcon interaction. Raptor 
Res. 12(1/2) :46-47. 

Ward. F. P.. and D. G. Fairchild. 1972. Air sac parasites of the 
genus Serratospiculum in falcons. J. Wildl. Dis. 8(2): 165-168. 

Ward. F. P.. D. G. Fairchild. and J. V. Vuicich. 1970. Pul- 
monary aspergillosis in prairie falcon nest mates. J. Wildl. Dis. 
6(l):80-83. 

Ward. F. P., D. G. Fairchild. and J. V. Vuicich. 1971. Inclusion 
bodv hepatitis in a prairie falcon. J. Wildl. Dis. 7(2): 
120-124. 

Webster, H. N., Jr. 1943. The prairie falcon in Colorado. Am. 
Falconer 1(4):10-13. 

Webster. H. N.. Jr. 1944. A survey of the prairie falcon in Colo- 
rado. Auk 61(4):609-616. 

White, C. M. 1962. Prairie falcon displays accipitrine and circi- 
nine hunting methods. Condor 64(5):439-440. 

White. C. M. 1963. Botulism and myiasis as mortality factors in 
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White. C. M.. and D. G. Roseneau. 1970. Observations on 
food, nesting, and winter populations of large North American 
falcons. Condor 72(1): 113-115. 



64 



Williams, R. B. 1942. Notes on the prairie falcon. Wvo. Wildl. 
7(1):12-15. 

Williams, R. B. 1943. Notes on hawk banding. Wyo. Wildl. 
8(12):l-8. 

Woffinden, N. D., and J. R. Murphy. 1977. A roadside raptor 
census in the eastern Great Basin, 1973-1974. Raptor Res. 
ll(3):62-66. 

Wolfe, M. L., and J. Neuhold. 1975. Density and species compo- 
sition of small mammals and birds. Pages 97-126 in U.S. Bur. 
Land Manage. Snake River Birds of Prey Annual Report, 

1975. USBLM, Boise District, Idaho. 193 pp. 

Wolfe, M. L., and J. Neuhold. 1976. Density and species compo- 
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Land Manage. Snake River Birds of Prey Annual Report, 

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Wrege, P. H., and T. J. Cade. 1977. Courtship behavior of 
large falcons in captivity. Raptor Res. 11(1/2): 1-27. 



Sharp-shinned Hawk 

(Accipiter striattis velox Wilson) 

Status: Appears to be recovering from earlier declines. 
Primary threat probably is the continued use of organo- 
chlorine biocides in Central and South America, which 
results in contamination of prey species. 

Original Discovery and Description: Falco velox Wilson, 
Am. Ornithol., Vol. 5, 1812, p. 116. plate 45, Fig. 1 
(Banks of the Schuylkill, near Mr. Bartrams'-Philadel- 
phia, Pennsylvania. American Ornithologists' Union 
1957. 

Background: The Pacific sharp-shinned hawk, A. s. 
perobscurtis Snyder, breeds in the Queen Charlotte Is- 
lands and possibly adjacent areas of western Canada and 
winters south to Oregon; similar to A. s. velox in size but 
darker, especially in juvenal plumage. The Mexican 
sharp-shinned hawk, A. s. suttoni van Rossem, breeds in 
the mountains of Mexico south to Michoacan and Vera- 
cruz and intergrades with A. s. velox in northern Mexico: 
slightly larger than A. s. velox, underparts paler, less 
brownish, and more reddish with considerably reduced 
markings (Friedmann 1950: AOU 1957; Wattel 1973). 
Easily confused with Cooper's hawk which, although 
larger, is very similar in appearance. 

A small woodland hawk preying almost entirely on 
small to medium-sized birds. Considerable numbers ob- 
served at various hawk-watching lookouts in central and 
eastern United States. Declines in recent years are 
attributed to organochlorine pesticides. 

Status Determination: Has been on the Blue List, an 
"early warning" list of species exhibiting potentially 
serious declines, since 1971 (see December issues of Amer- 
ican Birds, 1971 to present). 

Description: A small accipiter, characterized by long 
legs, long tail, and short rounded wings. Adults dark 
bluish-gray above, undeqiarts white, broadly barred 



with rufous or cinnamon, usually more rufous on the 
flanks. Females slightly browner above. Iris yellow- 
orange to deep red. Juveniles brownish above, underparts 
cream with broad cinnamon or brown streaks on the 
breast, diamonds or arrowheads on the abdomen, and 
barring on the flanks. Tail is relatively long and crossed 
with four dark bands. Iris pale yellow, claws and beak 
blackish. Adult plumage attained during second summer 
(Friedmann 1950; Wattel 1973). 

Sharp-shinned hawks exhibit considerable sexual di- 
morphism in size; females average 1.7 times heavier than 
males. Iris color becomes progressively redder with age; it 
is pale yellow in the first year, yellowish-orange to 
reddish-orange in the second, and deep red by the third or 
fourth year. Males appear to change faster and also attain 
darker red color than do females. Variation in intensity 
and rate of eye color change preclude establishing precise 
relationships between age and eye color (Roberts 1967; 
Snyder and Snyder 1974). 

Breeding sharp-shinned hawks characteristically use 
"plucking posts" ("butcher block"), where they deplume 
and partially dismember prey before taking it to the nest. 
These areas, with feathers and other body parts strewn 
about, are a good indication of nearby nesting activity 
(Brown and Amadon 1968). 

See Friedmann (1950), Brown and Amadon (1968), 
Wattel (1973), and birding guides for characteristics for 
identification of parts or products. 

Distribution: Breeds from Alaska and central Canada 
south to the southern United States, but scarce in the 
Southeast. Winters from British Columbia and northern 
United States south to Panama, the Gulf Coast, and the 
Bahamas (Friedmann 1950; AOU 1957; Wattel 1973). 

Habitat: Breeds primarily in the coniferous and mixed 
conifer-birch-aspen forests of the Canadian and Transi- 
tion life zones northward to the Arctic tree line. Less com- 
monly found in other woodland types in the United States 
except in mountainous areas. 

Nests are usually placed in trees with dense foliage be- 
low a well-developed canopy (Piatt 1976; Hennessy 
1978); conifers apparendy meet this condition most fre- 
quently. In Oregon and Utah, proximity to water ap- 
peared important, as did the more mesic conditions asso- 
ciated with north-to-east slopes (Hennessy 1978; Reynolds 
1978). 

Large concentrations of migrating sharp-shinned 
hawks occur in the fall and spring along mountain ridges, 
lakeshores, and coasts, which provide updrafts and serve 
as barriers to migration. On migration and in winter 
sharp-shinned hawks occur in almost any type of habitat 
containing trees or shrubs. 

Critical Habitat: Mixed coniferous-deciduous forest ap- 
pears important as breeding habitat (Piatt 1976). 



65 



Feeding Habits: Small to medium-sized birds (warblers 
and sparrow-sized species) predominate, and occasionally 
small mammals, insects, reptiles, and amphibians are 
taken. Mean weight of prey captured was calculated as 
17.6 g by male and 28.4 g by female sharp-shinned 
hawks (Bent 1937; Storer 1966; Wattel 1973). Storer 
(1966) noted proportions of 97% birds to 3% mammals. 
Sharp-shinned hawks use two basic methods of hunt- 
ing: still hunting from inconspicuous perches and fast, 
stealthy flights along paths and around bushes and trees. 
Thus surprised birds are taken by sudden, fast attack. 
Captured prey is almost entirely plucked before being 
eaten; favorite "plucking posts" are frequently used. 

Reproduction and Development: Nesting begins in early 
to late spring depending on latitude and, to some extent, 
weather. Adults may arrive at nest sites as much as a 
month before eggs are laid. Nests are usually constructed 
in densely foliated conifers and consist of small sticks and 
twigs. Nests are rarely reused; new nests are generally 
constructed in the immediate area of the previous year's 
nest (Brown and Amadon 1968; Piatt 1976). 

Little is known about mate selection in the sharp- 
shinned hawk; however, a recent study on a closely 
related species, the European sparrow hawk (Accipiter 
nisus) sheds some light on the process in accipiters (New- 
ton and Marquiss 1978). Six male sparrow hawks in mar- 
ginal habitat were followed by telemetry. Two spent all 
their time hunting over their entire territory and 
attracted no mates. Two others tended to concentrate 
somewhat in one area and attracted mates for 4 and 7 
days, then resumed hunting over their entire territory and 
within 2 days the females had left. The final two birds 
spent much time concentrated at the nest area, attracted 
mates, and eventually bred successfully. Apparently the 
ability of the male to secure enough food to remain in the 
nesting area and devote his time to courtship and nest- 
building is crucial to pair formation and eventual breed- 
ing success. 

Eggs, usually four or five, are laid in the late spring 
and take 30-32 days to hatch (Brown and Amadon 1968; 
Piatt 1976). Eggs are incubated primarily by the female; 
the male provides all the food and may attend the nest for 
short periods while the female is eating. 

The young are covered with white down when hatched 
and begin feathering out at 10-14 days (Brown and 
Amadon 1968). The male provides most of the prey for 
the first 2 weeks, after which the female spends increasing 
periods of time hunting as the young require less atten- 
tion. Young males fledge at about 21-24 days and females 
at 24-27 days (Piatt 1976; R. T. Reynolds, personal com- 
munication); they remain dependent on the parents for 
food for several weeks. 

Sharp-shinned hawks usually begin breeding when 2 
years old; the maximum known life-span is 12 years 
(Kennard 1975). 



Mortality Factors: Significant sources of predation have 
not been described; eggs and small young may be taken 
by typical nest predators such as raccoons, snakes, and 
crows. 

Sharp-shinned hawks have shown clear declines since 
the pre-1947 (pre-DDT) years. Analyses of sharp-shinned 
hawk eggs have shown exceedingly high levels of DDE 
(Snyder et al. 1973). Known relationships between DDE 
levels and eggshell thinning indicate that significant shell 
thinning is occurring. Although sufficient data on repro- 
duction are lacking due to difficulties involved in finding 
nests, indices of migrating sharp-shinned hawks show 
declines between 1947 and 1971, the years of heaviest 
DDT use (Robbins 1974). Although shooting was a signif- 
icant source of mortality when large-scale shooting 
occurred at various migration concentration points, it is 
now a relatively minor source of mortality for sharp- 
shinned hawks. Various accidents, storms, and factors af- 
fecting prey populations also contribute to mortality 
(Bent 1937; Snyder et al. 1973). 

Population Level: It is very difficult to assess the popula- 
tion level of sharp-shinned hawks. Data on reproduction 
and nesting density are lacking. Indices collected at var- 
ious migration concentration points (e.g. Hawk 
Mountain, Pennsylvania; Cape May, New Jersey; Hawk 
Cliff, Ontario; Cedar Grove, Wisconsin; Duluth, 
Minnesota) are subject to observer bias, lack of con- 
sistency of counts from year to year, and lack of standard 
observation and reporting procedures. Weather 
variables, which affect migration greatly, are difficult to 
assess in terms of magnitude of observed migration. How- 
ever, looking at long-term trends (Robbins 1974), which 
tend to average out weather variables, and correcting for 
number of hours of coverage, it appears that sharp- 
shinned populations declined, especially in the eastern 
United States, until about 1971. Data from subsequent 
years indicates an upward trend (Robbins 1974; J. L. 
Ruos, C. J. Henny, R. T. Reynolds, personal communica- 
tions) . 

Sharp-shinned hawks are relatively difficult to keep in 
captivity. A 1971 survey (Thacker 1971) reported two 
birds. An additional number, probably less than 20, are 
utilized for falconry. Captive breeding is technically pos- 
sible; little emphasis has been placed on breeding sharp- 
shinned hawks. 

Reasons for Current Status: Intensive forest management, 
particularly in western coniferous forests, results in large 
blocks of monotypic habitat, thus reducing potential and 
active nest sites as well as prey species (R. T. Reynolds, 
personal communication). 

The actual magnitude of the large-scale shooting at mi- 
gration concentration points is unknown but was most 
prevalent from 1895-1930 (Robbins 1974) and may have 
contributed to early declines. Protection from environ- 
mental contamination is limited to the DDT ban in the 



66 



United States. Large-scale use of DDT and other organo- 
chlorines continues in Central and South America. 

Organochlorines, primarily DDE, may be responsible 
for observed declines (Snyder et al. 1973). The DDT ban 
in the United States appears to have helped sharp-shinned 
hawk populations considerably (Robbins 1974); DDT 
residues in migratory songbirds (primary sharpshin prey) 
have been declining since 1964 (Johnston 1974). How- 
ever, large-scale use continues in Central and South 
America contaminating prey species that return to the 
breeding range of the sharp-shinned hawk as well as those 
in its wintering areas (Fyfe 1977). The proportion of 
sharp-shinned hawks wintering south of the United States 
may be considerable. Whereas 9 of 21 sharp-shinned 
hawks banded at Duluth, Minnesota, were recovered in 
Mexico and Central America during November through 
February, 6 of 9 recoveries were south of the United 
States in January and February. By March all recoveries 
were north of Mexico (D. L. Evans, unpublished data). 

Management Activities: Hawk shooting at migration con- 
centration points has been eliminated due to combined ef- 
forts of private individuals, Audubon Society, and law 
enforcement officials to increase public awareness. 
Sharp-shinned hawks are protected under the United 
States-Mexico Bird Treaty of 10 March 1972. 

The Hawk Migration Association of North America 
(HM ANA) is establishing standard procedures of observa- 
tion and reporting at the various hawkwatches in the 
United States (J- HMANA (l):l-2). 

See Snyder (1973) for current research on accipiters. 

References and Selected Bibliography 

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American birds. American Ornithologists' Union, Baltimore, 

Md. 691 pp. 
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Columbia. Occas. Pap. B.C. Prov. Mus. 17. 163 pp. 
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Part 1. U.S. Natl. Mus. Bull. 167. 409 pp. 
Bogan, J. A., and I. Newton. 1977. Redistribution of DDE in 

sparrowhawks during starvation. Bull. Environ. Contam. 

Toxicol. 18(3):317-321. 
Brooks, A. 1919. Sharp-shinned hawks and small birds. Condor 

21(5):213. 
Brown, L., and D. Amadon. 1968. Eagles, hawks, and falcons of 

the world. McGraw-Hill, New York. 2 vols. 945 pp. 
Brown, W. H. 1973. Winter population trends in the marsh. 

Cooper's and sharp-shinned hawks. Am. Birds 27(l):6-7. 
Chancellor, R. D., editor. 1977. World conference on birds of 

prey, International Council for Bird Preservation (ICBP). 

Taylor and Francis, Ltd., London. 442 pp. 
Cochran, W. W. 1972. A few days of the fall migration of a 

sharp-shinned hawk. N. Am. Falconers' Assoc. Newsl. (Hawk 

Chalk) ll(l):39-44. 
Craighead, J. J., and F. C. Craighead. 1956. Hawks, owls, and 

wildlife. Stackpole Co., Harrisburg, Pa. 443 pp. 
Daniels, G. G. 1975. An inquiry into Christmas Bird Count 

accipiter reports. Am. Birds 29(2):634-637. 
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tors. Part 2. Hawks. Condor 35(1): 19-29. 

Evans, D. L. 1977. Uncommon natural injuries in hawks. Auk 
94(3):585-586. 

Fisher, A. K. 1893. The hawks and owls of the United States in 
their relation to agriculture. U.S. Dep. Agric. Bull. 3. 210 pp. 

Forbush, E. H. 1909. The sharp-shinned hawk. Bird-Lore 11(2): 
94-97. 

Friedmann, H. 1950. Birds of North and Middle America, part 
XL U.S. Natl. Mus. Bull 50. 793 pp. 

Fvfe, R. W. 1976. Status of Canadian raptor populations. Can. 
'Field-Nat. 90(3): 370-375. 

Fyfe, R. W. 1977. Status of Canadian raptor populations. Pages 
34-39 in Proceedings of the ICBP World Conference on Birds 
of Prey - Vienna, 1975. 442 pp. 

Fyfe, R.'W., and R. R. Olendorff. 1976. Minimizing the dan- 
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Gray, L. 1961. Banding sharp-shins at Point Pelee. East. Bird 
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Greiner, E. C, and A. A. Kocan. 1977. Leucoctjtozoon (Haemo- 
sporida: Leucocvtozoidae) of the Falconiformes. Can. J. Zool. 
55(5):761-770. ' 

Hackman, C. D., and C. J. Henny. 1971. Hawk migration over 
White Marsh, Maryland. Chesapeake Sci. 12(3): 137-141. 

Hardy, J. W. 1971. Habitat and habits of the dwarf jay, 
Aphehcoma nana. Wilson Bull. 83(l):5-30. 

Hellbrekers, W. P. S. 1971. Communications on bird eggs and 
nests in 1971. Limosa 44(l/2):66. 

Hennessy, S. P. 1978. Ecological relationships of Accipiters in 
northern Utah — with special emphasis on the effects of human 
disturbance. M.S. Thesis. Utah State University, Logan. 66pp. 

Henny, C. J. 1977. Birds of prey, DDT, and Tussock moths in 
Pacific Northwest. Trans. N. Am. Wildl. Nat. Resour. Conf. 
42:397-411. 

Howard, R. P., L. O. Wilson, and F. B. Renn. 1976. Relative 
abundance of nesting raptors in southern Idaho. Raptor Res. 
10(4): 120-128. 

Johnston, D. W. 1974. Decline of DDT residues in migratory 
songbirds. Science 186(4166):841-842. 

Kellev, A., and N. Kellev. 1969. Porcupine quills found in foot 
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Kennard, J. H. 1975. Longevitv records of North American 
birds. Bird-Banding 46(l):55-73. 

Kilham, L. 1958. Repeated attacks by a sharp-shinned hawk on 
a pileated woodpecker. Condor 60(2): 141-142. 

Koeman, J. H., C. F. van Beusekom, and J. J. M. de Goeij. 
1972. Eggshell and population changes in the sparrowhawk 
(Accipiter nisus). Pages 542-550 in J. H. Koeman, ed. Side ef- 
fects of persistent pesticides and other chemicals on birds and 
mammals in the Netherlands. TNO Nieuws 27(10). 

Lloyd, G. D.,andC. B.Philip. 1966. The "wingless" fly, Camus 
hemapterus Nitsch (Milichiidae), on hawk fledglings in north- 
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Miller, W. DeW. 1909. A plea for the sharp-shinned hawk. 
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Mueller. H. C, and D. D. Berger. 1967. Fall migration of sharp- 
shinned hawks. Wilson Bull. 79(4): 397-415. 

Mueller, H. C, and D. D. Berger. 1970. Prey preferences in the 
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Mueller, H. C, D. D. Berger, and G. Allez. 1979. Age and sex 
differences in size of sharp-shinned hawks. Bird-Banding 
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42(3): 168-169. 

Murray, B. C, Jr. 1964. A review of sharp-shinned hawk migra- 
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67 



Bull. 76(3): 257-264. 

Newton, I. 1974. Changes attributed to pesticides in the nesting 
success of the sparrowhawk in Britain. J. Appl. Ecol. 11(1): 
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Newton. I. 1976. Breeding of sparrow hawks (Accipiter nisus) in 
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Newton. I. 1978. Feeding and development of sparrowhawk 
nestlings. J. Zool. 184(4):465-487. 

Newton, I., and M. Marquiss. 1978. Factors influencing the 
spacing and hunting ranges of European sparrowhawks. Pre- 
sented at 1978 Raptor Research Annual Conference, Allen- 
town, Pennsylvania. 

Norton, A. H. 1935. An exhausted sharp-shinned hawk. Auk 
52(3):304-305. 

Peeters, H. J. 1963. Two observations of avian predation. Wilson 
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Peterson, R. T. 1969. The contamination of food chains. Pages 
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iter. Publ. Nuttall Ornithol. Club 13. 231 pp. 



68 



APPENDIX 



Emergency Care for 111 and Injured Raptors 



1. Stop bleeding. If bleeding is severe, use direct pressure 
on wound. 

2. Contact a raptor rehabilitation center near you (see 
Raptor rehabilitation) or call your local veterinarian. 
Seek further instructions if possible. If this is not possi- 
ble, the following initial treatment is usually recom- 
mended: 

• The most critical problem is usually dehydration 
and starvation, not the wounds or broken bones that 
initially incapacitated the bird. Therefore, you should 
administer fluids orally, at a dose of 6 tablespoons per 
pound, every 3 h the first day. (Eagles weigh 8-12 lb 
(3.6-5.5 kg), great horned owls 2-1/2-4 lb 
(1.1-1.8 kg), and red-tailed hawks 1-1/2-2-1/2 lb 
(0.6-1.2 kg). The best fluid is Gatorade, because it 
provides glucose, phosphate, and salts. It is boiled to 
remove carbonation. If Gatorade is not available, use 
water (not sugared). Administer the fluid with a sy- 
ringe, poultry baster, small rubber tube, etc., but be 
careful to avoid getting fluids down the trachea (wind- 
pipe). 

• Immobilize broken wings by binding them to the 
bird's body snugly with gauze, cloth strips, or masking 
tape. 

• Place the bird in a dark box or dark room. Keep it 
warm. Put newspapers in the bottom of the box and 
cut slits near the bottom of the box for ventilation. 

• If you have to hold the bird for 1 or more days, try 
to feed it; perhaps force-feed it if necessary. Use raw 
meat (poultry or beef) or a fresh roadkill. 

• Advise a veterinarian to dose the bird with a 
broad-spectrum antibiotic (tetracycline or chlor- 



amphenical are good; give at the rate of 20 mg/lb in 
three divided doses daily). 

If the bird dies, freeze it as soon as possible to preserve 
it for valuable postmortem examination. 

Raptor rehabilitation: 
Dr. Pat Redig and Dr. Gary Duke 
Dep. of Veterinary Medicine 
University of Minnesota 
St. Paul, Minnesota 55108 

Jim Wisecarver and Gary Rogue 
Alexander Lindsay Museum 
Walnut Creek, California 97596 

New Jersey Raptor Association 

21 Spring Lane 

West Caldwell, New Jersey 07006 

Dr. John Lee 

Meridian Veterinary Clinic 

Meridian, Idaho 83542 

Tom Ruchanon 

2450 Glendale Avenue 

Abilene, Texas 79604 

Stillami Ure 

2322 Walker Lane 

Salt Lake City, Utah 84117 

Hope Carpenter 

R.D. 1, Rox 150A 

Mt. Rethel, Pennsylvania 18343 

Dr. Tom Thomas 

USAF Academy 

Colorado Springs, Colorado 80840 



As the Nation's principal conservation agency, the Department of the 
Interiar has responsibility for most of our nationally owned public 
lands and natural resources. This includes fostering the wisest use of 
our land and water resources, protecting our fish and wildlife, preserv- 
ing the environmental and cultural values of our national parks and 
historical places, and providing for the enjoyment of life through out- 
door recreation. The Department assesses our energy and mineral 
resources and works to assure that their development is in the best 
interests of all our people. The Department also has a major responsi- 
bility for American Indian reservation communities and for people who 
live in island territories under U.S. administration. 




UNITED STATES 

DEPARTMENT OF THE INTERIOR 

FISH AND WILDLIFE SERVICE 

EDITORIAL OFFICE 

AYLESWORTH HALL, CSU 

FORT COLLINS, COLORADO 80S23 



POSTAGE AND FEES PAID 
U.S. DEPARTMENT OF THE INTERIOR 



INT 423 




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